Crossfire 68/4500. All other HPA tank regs stink and aren't even worth mentioning.
Blue to Black Fade DM4
Empire Reloader B
72/4500 Crossfire Peanut Tank
Some other stuff...
The Crossfire 72/4500 Peanut tank is definitely worth the money. Most tanks, which I won't name, go for upwards of 300 dollars for a 68, which is longer and more hard to manuver than the peanut tank. The peanut also holds more air, which means more shots. The regulators on crossfire tanks are AWSOME. They are so consistent.
For it's size, air capacity, weight, and great regulator, this tank gets my vote!