If you have T-Mobile and an unlocked iPhone 4S, is the data really slow?

I live in Chicago so service isn't an issue. I'm just concerned not having 4G is going to be irritating… Also, I connect to Wi-Fi at home and at my university so honestly I maybe use data for 2-3 hours out of the day.

Do apps like Pandora still load easily?

Yes, definitely. Internet speed is mostly dependent on the device itself, not just how close you're standing to a carrier. The iPhone 4S has an a5 chip so the processor is quite fast anyway. It doesn't matter whether your width Verizon or AT&T, it will be pretty much the same speed.

If you think that Verizon is faster, it's probably because the satellite for Verizon is close to where you live so the signal strength is better. It would have nothing to do with quality then.

3G in general isn't that fast but it's bearable.