I work in morrisville/Cary area and I live in Durham. I have a nexus 4 on the $30 monthly 4g plan and tmobile seems to be very good. I have tested about 7-8 Mbps dl and ul around town. It even works inside the buildings. I have been trying to use sensorly so that it updates its maps. currently it does not show any coverage in places where I can get 10 Mbps download easily. Tmobile coverage maps seem to indicate good coverage in most of the town and it seems they have valid coverage maps.
Indoor coverage may be a problem as tmobile operates on 1700/2100 which is going to have issues inside buildings. Verizon and AT&T operate on lower frequencies and have better penetration however, wifi calling should take care of this issue for tmobile . Unfortunately, I have not been able to test this as nexus 4 doesn't support this however talkative and grooveip both seem to work great.
I don't travel to apex, holly springs, Fuquay area at all. I do go to Charlotte often and coverage is ok near the school (unc). I have also tested coverage in parts of Hickory and found tmobile to be pretty fast.