I've only ever tried BeerAlchemy and I don't see a reason why I'd ever switch. It has you covered from extract-only to starting your own brewery. I can't recommend it highly enough.
Beer Smith also has a Mac version. I started with the PC based version on my laptop and also have the Mac version on my desktop all for one price. You get 2 licenses ( I think) when you buy BS so you can have it on two different machines even if they are on different platforms. I'm very happy with BS. Very easy to use. Have never used Alchemy so can't compare the two. Sure you can't go wrong either way.