It depends, what you enjoy most, and how much time you are able and willing to commit. Cash games are obviously way more flexible than tournaments, and they are also more simple in the sense, that the blinds never change, and you dont need to worry about payjumps or ICM. A dollar won or lost is a dollar won or lost, and thats all, there is to it.
On the other side stacks are deeper in cash games on average, which create more complex postflop situations, where you are going to see the turn and river with plenty of stack left behind. This can make coolers like running two pair into a set more expensive and painfull, but it also allows you to get involved in some more advanced play.
Cash game specialist Nathan Villiams recently said, he find tournaments a bit boring, and I understand, what he mean. Because honestly the interesting and complicated postflop spots in tournaments are few and far between. With stacks quickly getting down to 20-40BB or less, tournament play tend to be a lot more mechanical. Especially when you get deeper into the tournament, there is a lot of raise-and-take-it preflop and then an occational rejam.
If you prefer the tournament format but cant devote many hours to an MTT session, SnGs might be the solution. They are still tournaments but over in much less time, depending what exact format you choose. As for profit potential in my opinion its highest in MTTs. But for learning cash games and SnGs are better, because they are less complicated overall.
