I prefer cash game, but if you start with a bankroll of 0$ you must start with freerolls.
In my opinion it is faster with cash-game, but you need a minimum of 25 buy ins.
If you play mid-stack-strategy on NL2 you need a minimum of 20$.
This 20$ you must earn on freerolls.
But is a hard way, becouse on freerolls you get a lot of suck outs.
A good way to increase your bankroll is to play freerolls from CC or you play the league on
pokerstars.
I start my own challange in februar this year from 0$ to 100$. After 2 month league at pokerstars my bankroll is current 13.79$