Answer to question:

When you have a big bankroll.

I love playing in MTTs, but the variance is so high that I have lost a good bit of money on them. The reason was I only had a br of like 2-300 and I was playing $10 mtts. Even great players can go for many many tournaments before they make a big cash.

SNGs are not as swingy as MTTs but they are still very swingy.

I would recommend cash games. If you multitable, the swings aren't nearly as bad as tournaments. My plan, as outlined in a thread in the Online Poker Rooms section, is to amass a substantial bankroll solely through beating cash games.

I would suggest you grind and whore your way up to about 2k before you attempt solely playing tournaments. And at that point still only play 22s and 33s maximum. With $2000 you could weather quite a downswing at those stakes.