If you travel internationally, The Nexus One is a great choice because it's GSM. You'll have to put up with T-Mobile/AT&T in the states, but when you're abroad, just pop in a foreign SIM card and you're good to go.
If you want the fastest internet with no caps, look at the EVO from Sprint. With 4G speeds from 3-6Mbps in about 2 dozen cities and a hotspot supporting up to 8 devices, you can almost use it as your only internet connection at home.
If you do a lot of texting/emailing, the Droid from Verizon is about the best Android phone around with a slide out keyboard, plus you get a reliable network to back it up.
I guess in the end you have to decide what you want and go from there...