Full ring teach you patience and waiting for good
hands. There are also less tricky postflop situations, because your average hand strength is going to be stronger. 6-max on the other hand is more action filled, because you are never in early position, where your range need to be really tight, and you also dont need to deal with situations, where someone else has opened from early position and have a very tight range.
Both can be profitable, so its largely a matter of personal preference. I will say though, that for cash games 6-max is simply more popular these days, and for tournaments its the other way around. So if you want to play cash games, you probably have to get into 6-max sooner or later, but you can still begin with full ring. And for tournament players there is no way around full ring games, since the vast majority of tournaments run in this format.