It's personal choice about what size you want.
Bottom line though, I'd stick with something by Kingston. It gets good reviews all-around, and I can say personally that I've never had any problems with mine.
I'd question the importance of the speed test thing too, because the second MicroSD I picked up was "Made in Taiwan," which is supposed to be slower then those "Made in Japan" and reportedly have problems with Portrait of Ruin. But after I finished griping about it and actually tested it, it worked fine with no lag.
So yeah, just make sure it's Kingston, I'd say.