Cash games are very different from Sit and goes, in that they tend to be more aggressive also it is so easy to let your money run away from you, with just a simple mouse click you can restack every time you bust out. The blinds never change unless you move to another higher table, and even if you bust out another player there is nothing stopping him from restacking and fighting back, So it becomes more of a grudge match with opponents trying to out do one another.
Sit and Goes are more like mini Tournaments each one is similar to playing on the Final table, and when you get down to the final 2 player it gives you the opportunity to practice heads up play, You are limited to how much you can lose in each game because they are set buy-ins and although you seem to be winning small amounts compared to larger Tournaments, they are good practice for bigger events.
The Rake from Cash games puts me off because they take their cut out of every hand played, where as in Sit and Goes the buy-in includes the Rake so you know exactly where you are.
I suppose it all boils down to Do you want to play Poker or just win money? Personally speaking I just enjoy playing the game, so sit and goes are my favourite, Winning money is just part of the game and means nothing to me as it all goes into my Bankroll.
I think that the On-line Poker boom has hit it's peak and now is in decline, with fewer players so the bigger games are harder to fill, PokerStars deciding to stop the
freerolls is just one example of how the On-line play is in decline.