What is the best electronic cigarette?

I don't want to spend more than $100. I read that the mall kiosks are rip offs and the ones on the internet are much better but there are still a lot of options. It's for my dad's 50th birthday (he's been smoking for probably 85% of those years) so it's very important to me that I get him the best for my buck so he can finally stop smoking! Thanks a bunch.