Online:
Most lower buy in tournaments are 500+ players making it harder to really earn some money since the prizes are rather small unless you get to the final table or near it, on the other hand, I believe that higher buy in also means different types of players against which it is harder to extract value, meaning it is also tough to make money unless you consider yourself a strong tournament player.
Live:
I know a lot of tournaments in my home town, with unlimited rebuy within some period of 5 or 6 lvls, try avoiding such tournaments, as people tend to gamble more to win a stack, and if you don't hit proper cards you just can't manage to build the stack.
If u just started to play tournaments, consider playing SNGs instead (similar structure as a tournament, less players, but unfortunately less money as well).