eSATA will always give best performance but a port isn't available on many computers yet. So if you are using the external with many PCs, USB will do you better. Why not get an enclosure with both types of ports like the new Silverstone MS05. I've got one here and have only inspected the product in detail preparing to review it - still waiting on the drive which I bought on FleaBay. So far all I'd like to see on it is some rubber pads on the drive enclosure itself for a little non-slip when using it as a portable. It's similar to the Vantec EZ Swap kits as it has a bracket to mount in a 3" bay or an adapter bracket - unlike the Vantec, it doesn't come with the 5" bay adapter.
.bh.