For beginners who want to study seriously and start building a bankroll
, definitely SnGs.
In it, you will learn the dynamics of a tournament: early stage, mid stage, bubble and heads-up, and also concepts like ICM, Nash Equilibrium, etc.
Here you can even play turbo single table tournaments, but it is better to look for at least 8 minutes
of blind levels.
But later, it depends on what are your goals. Let's say you want to be a MTT player: despite SnGs are quite similar, you will not be satisfied playing them in the long run. So, let's say you want to move to MTTs (because here are the bigger prizes, despite the bigger variance).
You can slowly increase the tournament number of players when you feel comfortable before moving to MTTs. There are many SnGs available with 18, 27, 36, 45 or even 90 players. So you can simulate how you would be going in a MTT, because this is what they are, despite being "sit and gos".
Here you will learn the dynamics of a final table.
Another very important thing, easy to say but not so easy to practice: when you are starting, do NOT
play too much tournaments with many people or turbo tournaments: the variance is too high. Give it a shot sometimes, specially if it's a special tournament with a lot of money guaranteed.
Look for regular tournaments with less players (like 300 to 500 players).
Patience is maybe the most important thing in the beginning.