Technically, both Maemo and Android run on Linux kernels. However, Maemo is a full Linux distro, based on Debian, while Android is a sole kernel with a few programs on top of it (namely, Dalvik virtual machine and Sqlite database). On Adnroid all applications run within Dalvik virtual machine, which is heavily optimized and modified version of Java virtual machine (JVM). I tried to analyze the benefits of each platform from the perspective of a software developer, as well as platforms' current "strategic position". If you are too busy to read all the details, there is a short summary paragraph at the end of each chapter.
Android vs Maemo from developer's perspective
Development.
Maemo SDK is Linux-only. It's not a problem for me (as Linux is my OS of choice), but it may be a problem for many developers. SDK works best on Debian or Debian-based distros (e.g. Ubuntu). Maemo is also a Debian-based distro, so SDK simply uses Scratchbox cross-compilation toolkit to build for both x86 and ARM architectures.
Maemo applications are developed in GTK+ using Hildon application framework. Naturally, the primary language of Maemo application development is C. Other languages can also be used, as GTK+ has bindings for many programming languages, including C++, Java, C#, Ruby etc. However, most applications will be developed in C, mainly due to performance constraints, which are especially actual for mobile devices. GTK+ itself is a bit archaic by today's standards, and although Hildon is specifically targeted for touch-screen interfaces, most of work is still done in GTK+ and good old C. Thus, the development platform is not on par with modern mobile application development environments such as iPhone SDK, Android SDK, or Palm WebOS Mojo SDK. This may change with Maemo 6 release (codenamed "Harmattan") when Qt libraries will be supported and Qt will become Maemo official application development framework. But this will happen somewhere in 2011, so for now Maemo application development is a step behind that of Android.
Update: As multiple commenters pointed out, Qt should be already used for Maemo application development. It's a modern way to develop cross-platform apps that will run on both Maemo and Symbian OS (as well as Windows/Mac OS X/Linux, although it may not be practical to use similar UI for both desktop and mobile software). The earlier Qt becomes official application development framework for Maemo and Symbian OS, the better.
Android SDK is available for Windows, Linux, and Mac OS X. Applications are developed in Java and the development platform is really easy to get into. It features XML (DSL) for GUI interface building, easy strings internationalization, app storage within SQLite database, background processes management etc. To make a long story short, it's how modern mobile application development platform should look like. The only downside is that all applications are in Java, and for some developers Java became the synonym of slowness (although it's not that slow on Android, as Dalvik VM is specifically optimized for running on it). For such developers, there is an option of using Native Android SDK, although its capabilities are very limited, especially in hardware access department.
Porting existing applications.
In this area, Maemo has a huge advantage over Android, as it's a full Debian based distro. With the help of Scratchbox Cross Compilation Toolkit many open-source tools can be compiled for ARM architecture. A number of command line utilities can be ported with a simple cross-compilation, GUI apps usually require UI rewrite, but anyway it's much easier to port open-source app to Maemo than to write it from scratch. Some of the famous open-source apps are already ported to Maemo: MPlayer, Pidgin, Gnumeric, Abiword and many others.
On Android, porting an open-source app from x86 Linux is almost as hard as porting an app from any other platform: all UI and logic has to be rewritten from scratch.
Summary: Development is easier on Android platform, while porting existing apps is easier for Maemo platform.
Strategic position
Both platforms are aimed at the same vertical market: smartphones – MIDs – netbooks. Maemo is backed by Nokia alone, while Android is backed by Open Handset Alliance, whose members include Google, Samsung, LG, Motorola, HTC, Acer and others. Nokia may be the largest mobile phone and smartphone manufacturer on the planet, but it cannot compete with such a might. Thus, it's obvious that in the nearest future Android devices will outnumber Maemo devices by a large margin. There should be 18 Android devices released by the end of the year, while there will be only 4 Maemo devices released by that time (Nokia N770, N800, N810, N900). Even if N900 and new Maemo MIDs, and finally netbooks will sell better than their Android counterparts, the total install base of Android devices will grow faster than that of Maemo devices. The larger install base, the more OS is interesting for developers (assuming, it has a decent app dev platform). Nokia's main competitors - Samsung and LG - will use Android as a competitive advantage, and throw their development and marketing efforts behind this platform. Motorola is trying to save itself with its MOTOCLIQ aggressive pricing and MOTOBLUR Android software, and it has the chances to succeed!. Under the circumstances, Maemo becomes Nokia's main competitive advantage, so the company should throw its efforts behind it or lose market leadership. The position of fierce competition ensures the bright future for both platforms. However, which platform will finally win is another question, and perhaps the most interesting one. The logical winner is Android: it'll have larger install base in the nearest future; more developers will work on apps for Android; it is backed by powerful corporations, mighty Google among them. Nevertheless, there is a single power that can keep Maemo up float and possibly even make it prevail in the long term: open-source community. You'd argue: both Maemo and Android are open source. It doesn't matter. What matters is whether the platform could benefit from countless man-years of efforts, done by open-source community. Android benefits only from Linux kernel development and a small number of other open-source projects, all Android apps have to be written from scratch. Contrary to that, any open-source project which runs on Linux indirectly contributes into Maemo software ecosystem (as it can be relatively easily ported). Maemo has to use this to its own advantage, or it has no chance against Android. Thus, Maemo core developers should make this advantage even bigger by easing the process of porting open-source apps to Maemo, which can be achieved by migrating from ARM to x86 at some point.
Another advantage of Maemo is that it's more suitable for larger devices - MIDs and netbooks. Maemo was designed to run on MIDs, and it already proved its worth in this area. Being a Debian-based distro, Maemo will probably fit well on touchscreen netbooks as well. Android looks good on smartphones, but it remains to be seen whether it will be enough for netbooks. There is a chance that Android will succeed on smartphone market, while Maemo will prevail on MIDs and netbooks.
Summary: Android has better strategic position at the moment: Android devices will outnumber Maemo devices in the nearest future, it will also have more developers (better development platform + larger install base). Still, Maemo can win after all if it plays nicely with open-source community and utilizes its tremendous work. Another Maemo advantage is that it's better for MIDs and netbooks.
Post scriptum
Either Android or Maemo, Linux will win after all :)
Post post scriptum
As much as you may prefer Android, Maemo, or other smartphone OS, the ideal situation for smartphone market as a whole would be healthy competition between a few major platforms, not a single platform dominance. Maemo and Android are both open-source and overly good operating systems, so it will be good if they become those dominate platforms, not killing each other, but competing in equilibrium for years, bringing innovation along the way.
Update
For more insights and opinions on topic, please read the comments below and the article's discussions on Reddit and Maemo Talk.
Summarizing the opinions, I've listed the following advantages of each platform:
Android advantages:
1. Binary compatibility between releases. Technically, it's byte code compatibility in Android's case. Maemo lacks it, which means hard time for developers with every new release.
2. Android is better positioned at mid-end smartphone market, where it will compete with Symbian OS.
Maemo advantages:
1. Better game development, especially cross-platform game development.
2. Qt can (and should!) be used for cross-platform development for both Maemo and Symbian OS, which equals developing with modern app dev framework for the largest smartphone install base.
