It's far far more important to buy from a retailer/site that will replace if it doesn't work. I would much rather buy from someone I trust such as OWC or Crucial or others and know that if there is a problem they will replace the ram. Ram can be touchy.
I'd look on newegg.com and see what the best deal is. Brand doesn't seem to matter a ton. I got crucial when I upgraded because I heard good things about it, and it was a good price.