You would want to get MicroSDHC (not MicroSD) because MicroSDHC is a new technology and is better in terms of speed and capacity.
Speed Guide:
Class 2 < Class 4 < Class 6
About brand, I don't know much to objectively judge the quality of memory card.
As long as they work everything else may be impression or psychology only.
Here is just my subjective comments.
It appears memory card from Japan is of better quality. People seem like to get them more.
Toshiba and Kingston is great.
Sandisk isn't good overall. Some are but some not.
A-data produces good and cheap computing RAM. I hope the same applies to memory card too.
Note: When a memory card says it is 4GB, it doesn't express in binary data size that the computer uses. The actual (binary) size is smaller. What a shameless marketing gimmick