I'd recommend the Galaxy S II - it's the most powerful phone currently on the market, has great battery life and a buttery smooth U.I, and is cheaper than the iPhone 4. It'll also remain current a for good deal longer than the iPhone as, if Apple stick close to their regular release cycle, the iPhone 5 should be coming out quite soon.
The Android Market just hit 200,000 apps, and Google have started to upgrade its search functionality, so finding quality apps should get much easier. On top of that, thanks to a recent deal between Google and a bunch of phone manufacturers and carriers (including Samsung), the Galaxy S II is guaranteed to remain up to date with the latest version of Android for at least the next 18 months.
Basically, the Galaxy S II is pretty much the best phone money can buy at the moment so, if I were you, I'd run down to my nearest phone store and pick one up while I still can.
(Sent from my iPad, just to prove that I don't have an anti-Apple bias or anything.)