Today I played a sit-n-go with the following situation: I find AJ offsuit in the small blind. Three people fold, the guy in middle position makes a standard raise of 3x to 90 total. Now I have 2 broadway cards with the ace, which I like as a hand. So I'm thinking that when it comes to me, I'll raise to 225 or something.
But then the cutoff calls. Ok, I think - then I'll raise a wee bit more. I don't wanna play AJ three handed, plus I still have the big blind to act behind me.
And then the button calls. So what does the nice little TAG in me do? Yup - I muck the AJ. After all, the only other option is to raise about a third of my stack, which in the sit-n-go format this early isn't something you wanna do with AJ. I can't call, since that'll be a 4-way pot and what if the big blind shoves on the 4 people. Fold?
So I muck it preflop. That's being a nit. And frankly, although I know it's the right way to approach these situations, I don't like it. I've played far too many hands by calling anyway, and then folding the flop (or worse, calling the flop and folding the turn, or folding the flop to a raise) and losing chips I shouldn't have lost. A definite leak in my sit-n-go play.

Last week I started dabbling in cash games. I played the 2NL fullring tables for awhile. And I noticed a whole different me. I'm raising pretty light, c-betting pretty light, and generally, it works. In 2 days I turned a profit equal to half a month's work at the sit-n-gos. Now of course the sample size is pretty low, so it could be just a few lucky rounds, but still.
I find myself more comfortable with the loose style of play I employ there. I lost a few big pots, but except one donk move, they were all allin situations where I got it in with the best hand and got sucked out on. Unlike the sit-n-gos, where I regularly find myself shoving or calling with the worst of it. It's the dynamic of the sit-n-go that forces your hand sometimes. So guess what? At the cash games, I'd label myself a LAG, not a TAG.

So which am I? Good question. Looking back at a month of sit-n-gos and a weekend of cash games, anything you say hasn't got too much validity, but I think I can point a few things out.
It looks as though the LAG style of play is more my style. Which also explains the results I have at the sit-n-gos. Although they're not bad, most of the mistakes I make are because I'm playing hands that in retrospect I shouldn't have played. The same hands that work for me in the cash games are my downfall in the sit-n-gos. The K10, the QJ, the KJ, the Ax, but also most suited connectors and suited one-gappers, any Kx from late position. So it seems that I try to play a TAG style in the sit-n-gos, but make too many LAG moves. And although a good LAG style might work there as well, you can't decide to play a TAG style and then start making the LAG moves. Maybe the pros can, but not me when you're as new to this as I am.

So, I have to work on the sit-n-gos more. Tighten up, everybody always says you should play pretty tight during the first several levels. I also have work on the cash games - play a lot more hours to see if the style of play there actually works, or if I was just getting lucky.

More food for thought, more pondering, and more lessons to be learned.