As far as batteries they will be similar in battery life. There are auto 510s out there. If you are concerned with battery life I would go to a bigger battery like an ego or riva. There are 901 Rivas if you do want to go with the 901.
As far as manual or auto. I like auto batteries, but I don't like that juice can get into the battery and kill it. I also don't like the automatic cut off times. The manual gives you more control on how long your draw will be, and there is no need to prime it like an auto. You can just press the button for a second before you inhale.
As far as the atomizer goes i prefer the 901 because the flavor is much better than the 510 IMO. The throat hit is greater on a 510 though.
It is really about personal preference, but I hope I gave enough info that you can make an educated decision.