Most choose to go overboard on torque. Nowadays, running off-road platforms on high traction surfaces will add to the stress/torture of a servo. A steering bellcrank not having a servo saver built in will need to be taken into account. I'm onboard with a lot of stuff posted earlier about torque, and speed ratings.

Watch out for High Voltage numbers in the specs if you are running a BEC that only puts out 6 volts.

A lot of times a manufacturer will have different tiers of servos. The lower end tier will be, more than likely, a disposable piece of garbage once it dies, or strips gears. I like shopping for the middle tier range/moderately priced stuff for my track bashers. You can find a good balance of speed vs. torque out there. I would take a servo with more torque than a servo with blistering speed. It all depends on where and how a person uses their RC car/truck.

One more thought...Not all gears are made the same. Aluminum, brass, steel, plastic, titanium....take that into consideration when servo shopping. Sure, you can find those low budget all plastic cased servos that have too good to be true specs, but why chance it? When I go looking for a moderately priced servo, I make sure to find one that has spare gear sets available.

When in doubt, go to specific RC platform thread, and ask what servo everyone is using...that in itself can be fun to see all the responses .