for mobile phone class 4/6 is enough..class 10 is necessary for DSLR..
if money is not a constraint go for class 10 else class 6 should be good enough..
i prefer san disk..as it is more reliable..and even at same class its performance is better than other cards...
also make sure you are getting genuine product..nowadays lot of sd cards are fake...
i bought 32 gb class 10 san disk for my tablet for Rs 1650...and 8 gb class 4 sandisk for my mobile...