Guys, I'm thinking of getting an Android device as my first smartphone. Noob here trying to explore the Android world and it's capabilities. Can recommend good device for a starter?

1. Brand: Any brand, but I'm eyeing for HTC.

2. Budget: 1.5k and below, may push to 2k but no further.

3. Specs:
- Have keyboard / keyboard+touchscreen (I don't like touch screen much, preferences are QWERTY keyboard).
- Can upgrade to latest OS, or at least above Android 2.0 (is there much differences between OSes? Links appreciated )
- Can put customize ROM; wanted to explore the Android customization to the max.
- Big screen for easy browsing.


4. What you need in the phone:
- Speed; at least no lag if running multiple apps (e.g run Twitter / FB and incoming calls, no lags. My current SE W508 lags like hell! Even SMS and then comes an incoming call can make the phone hang T__T )
- The best battery life under heavy usage (I wanted to hv FB & Twitter & chat apps to be on at most time, if can last for one full day is good enough).

I'm eyeing HTC Desire Z and comparing it with Samsung Galaxy 551 but I heard Samsung Galaxy 551 is hard to find now, is it true?