In order from most to least torque
rock crawling = the more the better at least 250 oz/in, speed doesn't matter than much as long as its below 0.20 sec
1/8 buggy/truggy = eh try to stay above 220 oz/in on steering, 150 on throttle, speed try to keep it under 0.15 sec
1/10 short course 4wd = 200+, under 0.15
1/10 buggy 4wd and sc 2wd and 1/10 stadium and 1/8 and 1/10 nitro onroad= 150+, under 0.10
1/10 buggy 2wd = 100+, under 0.10
1/10 tc onroad = 100+, fast as possible ex: 0.055

I probably left some categories out, just approx and personal judgement, in general for racing, the faster the better.
The servos that I think are good options
1258tg for any 1/10 offroad class $70 166 ozin, 0.08 sec
1257tg if you want a faster servo for 2wd buggy basically different gearing of the 1258
Team powers dcs/sgs for andy 1/10 class offroad or onroad. This is my favorite servo with 220 ish oz in of torque, its shorty so it saves space and fits in onroad and its 0.055 sec speed is op. Its a little price at somewhere around $120ish
In general savox is a safe bet on a budget, team powers is great, protek and mks not much experience but heard good things, traxxas is bad, any plastic gear is bad unless your on a really tight budget.