These threads should help you:-

http://androidforums.com/samsung-galaxy-s2/394060-class-micro-sd.html

http://androidforums.com/samsung-galaxy-s2/336953-sd-cards.html

Class 10 would offer you no benefits with the SGSII speeds.

Personally, I use a class 6.

Hope this helps.

 

i use a class 6 for my 15mp dslr camera, and ive never had problems with speed i dont think u'll have any issues using a class 6 with this phone in fact, i think a class 4 should be fine too

 

...and even Class 2 is fine for 1080p encoding/decoding...

 

Class 10 all the way. I just did a h2testw on a Class 4 32 GB and it took over two hours. It would have taken about 30-40 mins with a Class 10. When you are saving big amounts of files you will need to move them. And if you don't want to wait forever and a day I would go with C10.

 

just save video on phone and move it over to card

 

I have a class 4 Sandisk, and it works extremely well. HD video playback is perfect. No lagging etc.

If your loaded or your going to be transferring extremely high volumes of data between PC and card, then get the best you can by all means (I would have!!)

But for most people, a class 4 would probably suffice.