Which MacBook Pro do you have? Some are compatible with 8gb, some aren't.
If you have one that's compatible, you can't really go wrong with Crucial. They have a System-Scanner on their website which picks out the best RAM for your computer.
Ram technology nowadays is pretty good so any ram that you buy will be fine. Don't fall into the pitfalls of Extreme Ram, or Mac ram those are just marketing ploys to get more money. Just get the cheapest one you can find.