Intel is Native and ASMedia is not native and adds a fractional amount of latency as an add-on chipset. Otherwise the differences can be bandwidth, the native Intel will have full bandwidth whereas the ASMedia is shared. For most folks it won't make any difference.
ASUS offers 'USB 3.0 Boost' to the non-native USB 3.0 chipsets via 'UASP Mode' and requires 'AI Suite II' to function. A 'data buffer' is a fancy way to say the data is stored in the RAM (memory). I have found some of these ASUS 'tweaks' to be a dual edge sword, and anytime there's a power disruption with a 'cache' you risk corruption. See - http://event.asus.com/mb/2010/The_Best_USB3_Experience/The_UASP_For_USB3.0.htm
More info - http://rog.asus.com/forum/showthread.php?11986-What-is-ASUS-USB-3-Boost-and-UASP