USB 3.0 is, indeed, the better option (providing faster data transfer) as long as your laptop/PC has USB 3.0 ports. (Older devices might only have USB 2.0 ports). A USB 3.0 CD/DVD drive will still work with USB 2.0 ports though but only at the slower speed.
Like SA above, I'd also recommend buying a drive that can write DVDs as well as CDs. That means that you should see 'DVD+/-RW' (and NOT just 'DVD-ROM') in the description. This might be my choice at the moment:
Amazon.co.uk User Recommendation