Where do I start when I go shopping for a servo:
- Set a budget ($40~$60 my past normal servo budget)
- Are replacement gear sets available? (if the answer is no, the servo doesn't make my cut)
- Speed that I want (0.09~0.14 sec./60° my comfort zone)
- Torque that I want (depends on scale of RC, tires, servo saver, etc.)
- Gear material that I prefer (all metal, most of the time)
- Voltage needed to get speed/torque
I like shopping for the middle tier range/moderately priced stuff for my track bashing RCs. You can find tons of servos out there with a great balance of speed/torque. I would take a servo with more torque than a servo with blistering speed (to a degree of course). It all depends on where and how a person uses their RC car/truck.
Nowadays, racing off-road platforms on high traction tracks with not so forgiving surfaces, will add to the stress/torture of a servo. Sometimes tire size, and the use (or lack of) a built-in servo saver will need to be taken into account also. Most choose to go overboard with torque when choosing a servo (not a bad thing).
Targeting a group of servos with certain speed/torque specs? Watch out for 6.6v, 7.4v, 8.4v High Voltage servo specs

in the fine print so you are not totally caught off guard if you are running a speed control that only puts out 6 volts for receiver/servo.
Not all gears are made the same. Aluminum, brass, steel, plastic, titanium....take that into consideration when servo shopping. Sometimes not all gears in a metal gear servo are actually metal. You may have to dig deep into specs, and manufacturer's website to uncover some info

. That being said, if one of the servo gears is a plastic composite... not all brands us great plastic composites.
Everybody has their own opinion on what value means to them. Before shelling out money for any servo, I would need to have replacement gears available for purchasing if/when the time ever comes. I certainly would feel more comfortable spending $40~$60 on a servo, and know I don't have to throw it in the trash after many months of use just because of worn/stripped gears.
The servo choices back in the day were not like today's market. Today's market is huge, and, with all the re-brands out and about, it sometimes takes genealogy experts to track things down to their OEM origins.
A couple of my latest kits give servo torque suggestions in the manuals. 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 you'll get.
Super fast is not always better. Being in a high traction racing situation, and nerves getting the best of you, a fast servo may make your RC feel twitchy... possibly making you slower. If you have a radio that is more than the entry-level type, there is a good chance your radio can tame a wicked fast servo with different settings/parameters until you get to a comfortable track navigating speed.
After being in the hobby awhile, and following everyone's moves on interwebs, you'll soon pick up on “the good, the bad, and the ugly” when it comes to servos. And just like everything else out there, when shopping for the “best bang for the buck” type of items, praise & horror stories will will surface for all brands. Trends change. People jumping on/jumping off the next great servo bandwagon so fast nowadays.
Good luck!