I may be the only one, but I'm going to stick with Virgin because of their awesome customer service. Yes, you may have to speak to several thickly accented indians before you are speaking to the right person, but once you are, they are really helpful usually. My old triumph broke (think it was overheating, but not sure; bought it used), and after telling them it wouldn't turn on, they agreed to send me a refurb. After waiting 5 days to get the refurb (they told me they would overnight it), I got a month of service for free. Not sure how good T-Mobile is.
Also, the plan is much MUCH better on Virgin. I can go over 300 minutes a month without being forced to permanently change plans. The $30/month gives you 100 minutes and unless you change plans to a much more expensive plan, you cannot get more. And if you change to the more expensive plan, you are not allowed to revert to the $30/month plan unless you buy a new SIM card. Pretty ridiculous.