Completely agree on the TMO side. We were an AWS customer with several hundred lines of service and had horrific service. They would frequently provision BBs as "PDA" devices, effectively making the BB useless for email. Way too many issues to document here.
We switched to TMO for our BBs and have had great service. Although their coverage maps looks fairly weak compared to Cingualr's map, we've found quite the opposite. I would use the word "precision" to describe their domestic coverage. They do not cover the broad areas that Cingular and VZW do, but rather focus on precise locations. TMO has excellent international roaming, far above anyone else.
Not too long ago, AWS offered "unlimited BB email" while traveling internationally for an additional $20 per month. Sounds like a great bargain, EXCEPT that they cut down on several data roaming agreements. Before, we would pay per K when someone traveled overseas. Even though we didn't take advantage of that unlimited offer from them, we still lost several countries' email access. Oh yeah, those countries were billing $3.50 per minute for voice calls. TMO has a similar $20 offer, but does not cut down the number of countries where it could be used.
TMO's customer service is outastanding compared to Cingular/AWS and Sprint. It is really easy to deal with them, particularly after dealing with the terrible service from AWS.