The short answer is, whichever you think suits you best.
The vessels (tanks) all comply to the same safety standards, many are made by the same manufacturers and re-branded and the differences in weight and size are minimal.
The most obvious differences are in the regulators, although most do pretty much the same thing and at today capped rates of fire recharge rates are not really an issue anyway. Some are low-pressure output, (400 - 500 psi typically, some high-pressure (700 - 850 psi) and some are even a mid-pressure out put (somewhere between high & low). Some believe a high pressure output gives a more consistent recharge, others that a low pressure output gives you a few more shots per fill until the pressure in the bottle falls below the regulator operating pressure. In reality, there isn't really much in it.
One thing you might want to consider is the overall length of the bottle and regulator, if you have T-Rex arms go for a shorter set-up, if you have gangly arms go for a longer one, though this can usually be corrected by the position of the ASA on the grip frame/rail.