Use a class 10 SD card for best speed.
The USB bus can't come much higher than 30MB/s so you don't have to buy
any extremely fast ones though. Not all cards are compatible, check the compatibility list: http://elinux.org/RPi_SD_cards
Use the HardFloat version of Raspbian instead of the SoftFloat. HF has much faster floating point operations - however SF is required for running Java. So it's either Java or performance, like normal.