i do believe intels i3/i5/i7 line are still at the top, both in the editing and gaming world. it has a quick sync option which makes video editing and conversion much quicker, which helps in the encoding process.
Encoding software tends to take advantage of as many CPU cores as you can throw at them. So if you're going to be doing a lot of video encoding, a CPU which is hyper-threaded (or the AMD equivalent) would be better (eg i7-3770K). If you're going for a system where you'll occasionally encode but mainly game, then it makes little sense to spend an extra £100 on a feature you'll use once in a while, so an i5 CPU would make more sense (eg i5-3570K).