Well that depends. Are there any pre-evolution moves you want or need? Then go until he/she learns those moves.
Okay it depends gliscor has the early elemental fang benefit however and his pre evo moves are only slash and poison sting which arent worth it how ever gliscor would be harder to train since hes evolved especially at a earlier level. So yeah i would train it as a gligar since training is easier then evolvev it around lv 30+ and give it elemental fangs through move remembering tutors.