I use Sandisk and PNY...no issues with them...again Dan hits the point if you need the fastest card then get it, everything else will just not do...but for everyday shooting or less stressed shooting...anything over x200 or 30mbs should be ok...
Now if you are going to do video, or move to it later...the faster the card...the better off you will be...
Benchmark Access Times... <--- This is at the end of the article I found...but the whole thing is acctually really informationve about I/O speed and Read/Write times...should be all you need to make your decision...
Also...I follow the rule of more...I would rather have 2x8gig or 4x4gig instead of just one 16gig card...now I do have two 16gig cards that I carry not for shooting but as a back-up for my shooting cards...I make a copy of the images on the other card, just in case...
Hope this helps a little...