This really is quite personal.
I've played 8 characters to 50 more or less at the same time.
Playing three planets or so, switching to another, then the next and so on.
Taking turns rep/empire side.
Worked fine and I'm not burned out at all
got a new set of five little alts that I take turns playing, although in a slightly less structured way. (felt a little put off only when four out of five had Taris as their next planet, more for a lack of choice than being bored)
For me the switching kept me from burning out.
Of course I never started grinding dailies, just logged in the next alt.