MTTs are extremely poor for bankroll building, because variance is large, they require a lot of time commitment, and there is not enough game selection, if you have a small bankroll like $100 or $200. So the choise is still between cash games and SnGs. And while SnGs have clearly become tougher, than they were 15 years ago, so have cash games.
So at the end of the day its largely about personal preference. Try both and see, which format you like more, and then make a choise. Some sites like GG Poker and 888 Poker dont even give you a choise, because they dont even offer SnGs. So if you want to build a bankroll of those sites, there is no other choise than cash games. When you have $500 or so, you can consider moving to MTTs at least during weekend and holidays.