With shorthanded SNGs you have to make many more pre-flop calls and post-flop decisions which often depend on your reads. I played a lot of these about a year and a half ago and they vastly improved my play, but as far as long term money in concerned, 10 person SNGs allow you to play more tables and make more automatic decisions, increasing your hourly rate.

I can't imagine playing more than three shorthanded SNGS at once. So, if you're playing for fun / to learn, they're awesome and will build your bankroll. If you're playing for the cold hard, pay-my-bookie cash, they might not be the best option.