Best microSD cards, that may be found today at stores is UHS-I with sequental read/write speed about 80-90 MB/s. To achive this read/write speed cardreaders must support at least UHS-I standard and be connected using fast interface like USB 3.0 or better. Use of old readers will reduce speed to about 20 MB/s. Use of USB 2.0 with UHS-I reader gives about 40 MB/s
Cards:
SDSDQXP-032G-G46A Sandisk Extreme PRO MicroSDHC (633x) UHS-I U3
TS32GUSDU3 Transcend ULTIMATE microSDHC 32GB (633x) UHS-I U3
SDCA3/32GB Kingston MicroSDHC 32GB UHS-I U3
Cardreader:
Transcend TS-RDF9
Software:
CrystalDiskMark 5.1.2 x64
Additional reading for topic:
http://www.cameramemoryspeed.com/reviews/sd-cards/
https://www.sdcard.org/developers/overview/bus_speed/index.html