If i were to choose my main right now, i can't choose one so it's 3 jobs : GNB, DRK and WAR since i wanted to tank during shb. I think having more than 1 main in the same role is very practical if you like to play savage/extreme and keeps things little more fresh. I even play PLD sometimes.
As dps i play drg and ninja the most but only on easier difficulties. Even if reaper becomes my new main, i will play drg too.
So i don't think you have to keep 1 job tbh, it's great to change a little bit sometimes. Ofc it depends on what content you do and how you do it, in a static you can't always change what you play. I don't have a static but if i had one, i would avoid playing with my static job as mutch as possible outside of it if it gets boring.