i think i have good training spots for infighters 1-70 =]

Personally, I did something like this:
10-15: Job-related quests (Mostly hunting pigs and green mush.)
15-20: Hunted Mano outside Lith Harbor
21-30: ACPQ, trained on Sand Rabbits and Jr. Cacti. Lots of Ariant quests will give great EXP.
30-35: Stumpy in Perion (the quest gives like 30% at level 35), Scorpions and Sand Rats in Magatia's desert. Also tried Cube Slimes and Rumo.
35-45: Iron Mutae at Magatia labs.

for 45-48 i've mostly done events and things that won't even possibly be an option for GMS.

well, if acpq = ariant then yeah thats an idea but i didnt add that cuz i forgot but now that ya mention it, it seems slow because if you dont win u get low exp and id just say if u choose to do that have a friend let u win or trade so u get alot of exp

and for rabbits i completely forgot about them! great spot nice spawn and mobs, recently trained a low level there for testing

now for Mano and magatia we might not get that in gms for a while so that is also something to take into consideration but i guess that one quest would be good xD