I find the atlantis shines around 36w, so a 50w box is a good call imo... as for sugestions - can't say it'll last as I've only had it a week, but the smok xpro m50 is a nice fit for the atlantis - not sure if it is my imagination, but my vape time off of it seems to go on forever with a samsung 25r in it - it might be the smallest 50w I have come across - got mine at a b&m for $60, so it was easy on the wallet as well. I would also recommend checking out the rDNA40 if you want something that's a little more upscale - 40w should be plenty for an atlantis - I have the 30w version and it is built to last for sure.