Apple-branded RAM is always best, though I've not had a problem with properly-spec'd 3rd party memory over the years.
Just out of curiosity, how much RAM do you have in your system currently? For a brief time I moved up from a 2GB Core Duo iMac to an i5 iMac with 4GB, and all OS X did was give more RAM to existing programs (for example Safari would take up over 800mb instead of 450mb with the same number of tabs), so I ended up swapping at roughly the same workload as when I had 2GB. I might be a unique case, but just thought it was worth mentioning. If nothing else, it convinced me to get at least 8gb in whatever new Mac I get down the road.