I have dealt with both powernotebooks and proportable. PN has great pre sales support, but they outsource thier techsupport, who I had to deal with twice, and I hate to say it, but they really were not very knowledgable at all. And had quite a bit of attitude to boot. But pre-sales was great, very knowledgable and friendly. That said, Justin who owns proportable routinely steps in on techsup issues and helps out himself. Pricing seems to be better over at PN though, but not by a large margin. Last I looked, its been awhile, dont take my word for it, go check them out yourself.
I like proportable quite a bit as well, and heartily recommend them. The extra cost is worth the service, IMO.