the following considerations are important. remember, a chain is as strong as the weakest link and so when buying a microsd card, you have to think about how you will be using it.
0. i have named this factor "0" because i am myself not sure about the kaiser's performance when it is INTERNALLY accessing your storage card. as far as i know, the kaiser's internal access speed is nothing to write home about even with the fastest cards. i'm hoping someone else can comment and shed some light.
1. do you intend to perform heavy data transfers to/from your device/pc using:
a. activesync?
b. card reader?
if option (a), a fast card won't get to show its full speed because the usb port on the kaiser does NOT run at full USB2.0 speeds. in fact, the SLOWEST card completely saturates the activesync connection.
if option (b), a fast card will make a noticable difference. but then you have to think about the following.
2. the card will understandably be used for READ operations and performance will be important in that aspect. if WRITE speed is important to you because you will be frequently dumping data into the card, then check up the write performance of the card(s) you are considering.
3. other aspects to consider are warranty, reliability, brand name (if you are so inclined, most things, even from the best brands, are made in china any way, probably at the same factories some times

)
good luck!