pweeSo the easiest would be scout? Roamer requires timing and knowing what to kill.
Why wouldn't be roamer
Becoming a mediocre roamer is pretty easy, which is why lower divs are flooded with mediocre roamers. Learn to bomb medics and BOOM you're a mediocre roamer.
Becoming a good roamer is tough, which is why there are relatively few great roamers. My last season in 6s was sort of a wake up call, since I finally started to understand that the roamer is the "wetworker" of the team, doing all of the ugly stuff that isn't noticeable to the casual eye. Is it time to be the "big brother" on the flank? Is it time to be the vanguard on a push? Is it time to be the clean-up on a push? Is it time to hide, or time to bomb?
The realization basically paralyzed me for a few weeks because I couldn't think and act fast enough to do all of those jobs at the same time, so I was basically doing none of them. By the end of the season I was starting to be able to do some of those jobs more effectively, but by then the team imploded and my personal life went bonkers.
It's similar to the transition for medics. The line of progression I've seen from a bunch of medics is that they go from "bad" to "decent" disproportionately fast, but the transition from "decent" to "good" takes a really long time. I think it would come down to getting the mechanics down, which lifts you into "decent" range, but from that point it becomes more about intangible qualities.
As a low-open shitter, this is one of the few topics I feel I can give insight on.