The Nova is a tank - simply put. I've hunted ptarmigan in northern Quebec with it in the winter - 40 below, no issues. I've brought it home to the Labrador coast and beat the crap out of in the sal####er - no issues (wipe the barrel with some oil or it will rust quickly). I've dragged it through the mud in the fields of Quebec, eastern and western Ontario, and it never skipped a beat. To me, it's the only pump on the market that can rival the BPS and the Wingmaser, and it is easier to clean than both.
The Super Nova has some differences - some good, some bad. Good - fit options, as mentioned before. You can adjust the LOP, DAC, and the cast on the Super Nova, making it fit you better, whereas if the Nova didn't fit, you were S-O-L. The stock is more gimmick than anything - I compared the one I owned (briefly) to my Nova with a slip-on Limbasaver and the Nova actually had less felt recoil - and that's without the mercury cylinder in the stock. Bad (some opinion, some fact) - it is bulkier in the hands than the Nova. It costs $100 - $150 more. The first run of the SN had many reports of lift-rail problems and trigger failures (the trigger pull is way too heavy on both, IMHO). I see fewer reports on the waterfowl forums in the States, so I will assume Benny has addressed some of these issues.
It's really a toss-up between the two. The way I look at it, if the Nova fits you, toss a $30 Limbsaver on there in the LOP you want and save yourself $100. I've owned both - the S Nova I had was one of the lift-rail problems. I hunt neither now. When you get into Super Nover money, you're in BPS money - the BPS is a much better built, more reliable gun, from a company that has a much better customer service reputation. My 2 cents on it - hope it helps.