If it is just for storage and you not writing much don't worry buy cheep.

If you copy date on a off as I do class 6 and above. I have found that not all class 6's are equal. The brand name is usual faster and natural more expensive. So if you subscribe to the notion that time is money you want the higher class.

I suggest reading the reviews on amazon someone inevitably has done a direct comparison between apples and "apples"

I hope ypu will repott your findings, so we can profit from your labours

I would recommend class 10 if u gonna isntall Nitdriod and maybe dualboot MeeGo in the future

for 70cad i was able to find Kingston 16gb class 10 card , so far it works flawlessly and it is fast comapred to my old class 6 card and has lifetime warranty

Ignore the class rating. Higher classes (espcially class 6) on microSDHC tend to be less reliable, leading to corrupt transfers, or shortenend life. Also, Class 6 (or higher) is generally something you need for high end cameras or HD camcorders due to the transfer rate.

For media playback, Class 2 is more than adequate. When transferring files, if you're using a card reader, you'll notice a difference between class 2 and class 6.

In summary, avoid the class 6 cards. They're overpriced, less stable, and are intended for professional recording. You'll get no benefit from using one over a class 2 in a PMP.

Source: http://icanhaz.com/speeds

RafaLL92, I really do not understand how to do "professional recording" on a "less stable" storage. Does a professional will take the risk to lose 4 hours shooting ?

Concerning swap usage, I agree a flash memory lifetime will be shorten compared to standard storage. I comes from its internal behavior: copy/paste block content as it is not able to replace a single 1 bit to 0, and it is only able reset a full block to 0. There is also a block rotation thanks to address mapping: a free block is reset to 0, content is copied (bits 1 are set) and so on at next block write access.

As a consequence even if you think you only use a part of your microSD as swap, in fact all internal blocks of flash memory are used and that means the whole card life time shortens.

i read on engadget the other day, on an article about windows phone 7, that manufacturers tweak the higher class sd cards for sequential speed, but it sometimes (often?) affected the random access speed negatively.
unfortunately, windows phone 7 operating system is too new for a decent list of compatible (high random access speed) cards to be available officially. you might want to try here or try googling yourself.

ref