I've used Pinnacle Studio 12 for about six months, and been extremely impressed with it. IMHO it has the easier interface. It's extremely intuitive, and makes splicing and other basic editing a breeze. It also has some nice, clean rendering controls.
I just began using Sony's Vegas last week, out of curiosity, because I'd heard many great reviews of it. The jury is still out, but so far my impression is that it's certainly a very nice product, yet a hair more frustrating to use than Pinnacle. I do like Vegas and am definitely going to give it a chance to grow on me... but so far I just haven't discovered any features which set it clearly above Pinnacle, to make the (slightly) less intuitive interface worthwhile. Again, I'm new to it, so I may very well discover that I'm wrong!