I know very close to feck all about Androids, but did fancy having one when I upgraded recently. I can't remember the make, but the cheapest I could find was stuck on an old version of Android, 1.x, with no sign of the manufacturers providing an update. Might've been the LG GW620.
So when you're looking, make sure you can get a fairly up-to-date version of the OS or can upgrade it later.
I ended up with a Nokia 5800 on an 18-month contract. Hopefully Androids will be a bit cheaper when this contract's up.
Got my girl a HTC Hero recently and very happy with it. Been thinking about another one and the cheapest deals, fleabay, appear to be with the tmobile pulse. Not the best but cheap and seems to do all you want.
My Android experience so far is the Pulse (1.5), Desire (2.2) and Wildfire (2.1).
I love Android and have to say that they are all excellent phones. Obviously the 2.2 Desire has features that make it the best phone, can't wait for the Evo in this country, I WILL HAVE ONE
Depending on what you want from a phone, there is really no major difference, a bit of speed, some different resolutions etc.