frustrated TMobile customer- alternatives?

A couple weeks ago I decided to go ahead and upgrade my plan with T-Mobile to include data and tethering service so I would have access to Netflix and such wherever I am if I don't happen to be at a Pilot/FJ/Petro/TA with good wifi or for whatever reason I'm out of points on my loyalty cards.

The data speed is extremely hit or miss. Sometimes it works fine, but more often other times (like today) the best I can get is the equivalent to dial-up speed which means when trying to watch Netflix I can watch five minutes of movie/tv show and then wait 15-20 minutes for the buffer to rebuild so I can watch another five minutes and do it all over again.

I think for an extra $30 a month its not too much to ask that my data be fast enough to watch Netflix without being interrupted every five minutes or less, especially when T-Mobile is supposed to be the one Carrier with speed capabilities that match Verizon.

Now, the phone is an older one, and not 4G capable. Its a Nokia 5230, and I've had it for a while. Still, even 3G speed should be sufficient for watching Netflix, and I should definitely be getting more then 20-40kbps average according to CNET's bandwidth tester (average download speed according to the phone itself is even less, usually 5-20kbps).

I am very close to terminating my contract with T-Mobile and switching to Verizon. I don't want to do that, I've been a TM customer for many years and they have outstanding customer service, but this is ridiculous. For what I'm paying per month for the tethering service I expect it to actually be fast enough to be useable.

I do not believe the problem is my computer- its a fairly new machine, Pentium dual core 2.2ghz processor, 3g of RAM, and Windows 7. I also know for 100% fact that my data speed is not being throttled due to overage- not even close.

I think it might be time for me to part ways with TMo and switch to a different carrier because I've already had enough of paying extra $30 per month to have data coverage that is hit-or-miss at best.

So...those of you that use either data tethering through your phones or USB modems/aircards...who offers the most reliable data service with the best lower 48 3G/4G coverage (if I'm gonna drop the bank on a new phone it will be something 4G capable)?