I have a mega and they are fantastic little devices. The 0.5 ohm coil is definitely a warmer vape, as well as a much bigger cloud, so go with the 1.0 ohm coil. It's the one I prefer.
You might also consider the 1.0 ohm CLR coils, not so much for replacing the coil (which is fiddly), but mainly for easily replacing the wick.