If you really want to be a professional poker player someday in the sense that you use poker as your main source of income to put food on the table, then I highly recommend you play cash games. I haven't conducted any studies, but it seems like the overwhelming majority of players who successfully play poker for a living, do so playing cash, ring games, not tournaments.

For starters, compared to cash games, tournaments are very high variance. Imagine you're in a cash game and get 100bb allin pre-flop with AA and lose to KK. If you play enough hands, 80% of the time you'll win that big pot for a nice long term win. It's no big deal when you lose 20% of the time because you just reload. In a tournament, on the other hand, you'll still win 80% of the time, but that 20% you lose can be a lot more devastating if it bursts your bubble and you don't cash or keeps you off the final table or even keeps you @ 2nd place instead of 1st. Consistent cashing is an important skill with tournaments, but more so WINNING is important and there is a lot of luck involved to be able to survive a tough, deep field and win the whole thing.

Outside of the variance, tournaments are more difficult in terms of logistically complementing your life. For cash games, you can just show up at a casino or fire up the computer online any time of day and play. You show up when you like and leave when you like. In tournaments, you show up, leave, eat, sleep, and go to the bathroom entirely on THEIR schedule. Say you're tilting in a cash game. You can take a short break, a long break, or just leave and come back tomorrow. At a tournament, you can't deal with tilt like that.

Don't get more wrong. Tournaments are fun. I started with tournaments. Tournaments were the reason I got into poker in the first place. They are very fun. But as it relates to generating money, by comparison to cash games, they are a novelty.

Having said that, if you can't be persuaded otherwise, there are some players who have found a way to play tournaments and make a living and most of those players are online. It can be done, but it'll take a lot of time, study, and patience. Good luck either way.