I've researched this very thoroughly over the past few weeks, and this is what I came up with:

1. If you want a physical keyboard, either get the Motorola Droid (in the USA)/Milestone (same thing rest of the world), or wait if you're not keen on this device. The keyboard is apparently an either love it or hate it kind of thing so definitely try it before you buy it.

There is also the Samsung Galaxy S Pro with a keyboard available on only one US carrier (IIRC, Verizon).

Personally, I'm waiting for a better Android with a physical keyboard.

2. If you want/don't mind a touch-only experience, then you got plenty of choice. The top end is the HTC Desire, which is very good (a die hard iPhone fan friend of mine is now a convert). HTC do cheaper and lower spec'ed devices too like the Wildfire so have a look at those.

If the screen is your top priority, the Samsung Galaxy S is apparently the one to get. But Samsung masacared the Android UI with their own "improvements" which you may or may not like. Check it out.

Finally, if you want the biggest screen, the Dell Streak clocks in at 5", which may be a touch too big for your pockets. I have big hands and loved playing with it at the shop but I didn't buy it because it is so darn freaking big. I suspect you'll find it to be too big too.