On the Desire you are covered with 1 and 2.
cant say about 3, but I have heard that batterytime is awful on it, even comparing to N900
Games are on all Android phones great IMO. Messenger is not as good as N900 ( but not by far) and browsing is also somewhat off, even though there is flash 10 on newer android firmware. The overall browser experience is different than n900, you either like it or hate it. I like the n900 .

On Galaxy, you have more balanced package, battery is similar to n900. Might even better, I don´t really know.

It all comes down to what you REALLY want, more apps/games in a more mobile phone package or less apps/games in more mobile computer package. All the 3 phones have there weakness and streights.

Just my 2 cents