I recently picked up a Samsung Galaxy S2 and I have to say so far I'm impressed. Although I prefer HTC's sense UI Samsung have definitely done something right with the S2 and touchwiz. Its speed and smoothness makes it simply a joy to use, no fumbling around with missclicks or annoying waiting while it loads. From what I've read it's the best Android phone on the market and I certainly wouldn't argue with that.
The 1.2 GHz processor realy shows through with everything you do. From streaming movies to web browsing everything is just so darn fast. The AMOLED screen is crystal clear even outside and the battery life is more than acceptable for me - I found the battery to be lasting around 2 days with moderate use.
You might be wondering why I chose Android over the increasingly popular iOS on the iPhone 4. The reason is that, as far as I'm aware, you cannot develop apps for the appstore unless you have a Mac, whereas Android apps are Java based and allow me to develop for the platform on my Windows computer. This, along with the slightly-larger-than-most 4.3" screen, is what made up my mind.
Now I haven't owned an Android based phone before so don't have many apps yet. Does anybody know any must-have apps that I should be getting? It seems like it's got everything I could possibly need already installed, but I'm sure it will have double that installed on it by the end of the week!