Another Vote for OmniFocus
I use OmniFocus with my Mac, iPad, and iPhone. Never had a problem syncing and once you get through the learning curve and set things up the way you like them, it is truly a delight to work with. Yes it is expensive, but when something works the way it is supposed to, and the way you do, then I don't care what the cost is.
I have tried Todo, but syncing always gets messed up in someway. OmniFocus it just seems to do it flawlessly. Many of the other to do apps I've tried were also good, but failed in someway that OmniFocus has always shined through. I've tried many different programs. Todo, Toodledo, 2Do, Pocket Informant, Wunderlist.
I do use BusyCal, mainly for the calendar functions and I do have my repeating tasks in there as well. My main task manager though is OmniFocus. If you go with OmniFocus or want a netter insight of how the program works I highly recommend watching the tutorials on the Omni Groups website. I decided to go with OmniFocus after watching those videos, plus I believe that they offer a 30 day free trial for the Mac version.