While most upper will work with a standard carbine buffer, most will also work with an h or h2. For the sake of your gun not beating itself up more than needed, I've found its best to use the heaviest buffer that your rifle will reliably function with. I personal am a big proponent of the vltor a5 buffer system. Not the cheapest setup around, but it is the best. I also run lots of products from v7 and it's all top notch. If you don't have plans to build an ultra lightweight rifle, tho, a lot of their product line would be pointless. Their standard 7075 receiver ext is every bit as good as a vltor, bcm, ect I'm sure.
If you got the funds I would say the vltor a5 system is best, in regards to a regular carbine tube just get a standard 7075 tube from a well regarded name and an h buffer and it will most certainly function fine. Once you shoot your rifle a bit you can start tinkering with buffer weights and such.