What are the best Internet cellphones?

I have a Sidekick Slide and before that a Sidekick 3. I don’t own a personal computer so an internet phone is nearly a neccessity. My 2 year contract with T-Mobile is almost up so I might move on if I can find a better service and phone. I never really liked the Sidekicks. They make surfing the web easier but I hate their limitations: not being able to watch video, not very fast, not being able to view certain pages, having to go to email just to receive pics, bad signal strength, not being able to download anything except their exclusive stuff that sucks, and a host of other shit. I did however get comfortable with the $70-$80 bill that I pay every month for unlimited access. But I need YouTube!

So what other phones can I choose from with better internet and functions than the Sidekick, preferably with inexpensive plans?

iPhones are primo for YouTube above all other internet phones.
Plus, despite being balls slow, their wifi connection is faster than T-Mobile’s.

Iphone is Sprint right? So ill probably be stuck with a high ass bill lol?

Are there any good Tmobile phones? Is TMobile even a worthy service?