Reactor is more efficient, it heats water more quickly and has the big advantage of being windproof. I have both and often take the Jetboil as it is a nice compact unit and I have the adaptor to let me use it with a normal pan. Whichever you use, you need to be aware of your gas usage so you don't run out. Easiest way I know to measure how much is left is to float a full can in water and mark the water line, do again when empty and the gap is your gas, so easy to mark halfway etc. Then use the empty tin as a template for new ones. Doesn't matter I guess if you never go too far from gas shops but important if you do.
I always store one of the diddy cannisters inside either the MSR or Jetboil as a spare. Not that I fancy balancing a towering Jetboil on one without the base support feet thing fitted.
Nothing like firing up that silent, radiant Reactor burner on a cold morning to warm your tent porch up!