Mud takes WAY more winching force than rocks will, its always better to overestimate than underestimate.
Spur gears or planetary gears are just different ways of getting gear reduction.
Here's what a spur gear design winch looks like:
Warn 8274's use a spur gear design to get their gear reduction which keeps the spool cooler (i.e. good for synthetic rope). You don't hear much talk about any spur gear winch than the 8274, but it likely has the best reputation of any winch ever made. Super fast line speed, great reliability and an underrated 8K rating (pull another 8K winch next to an 8274 and tell me they are rated for the same pull strength

). Warn has used nearly this identical design for ~50 years, its the standard by which any other winch is compared.
Here's what a planetary gear design winch looks like:
Most modern electric winches use a planetary gear reduction which makes them more compact and lighter but Warn doesn't recommend using them with synthetic rope because heat from the motor can melt the rope. There are lots of great winches that use a planetary design.
What I was getting at is that you can't really hide a spur-gear type winch like an 8274 behind the grille, its bigger (and heavier) than planetary winches. It blocks plenty of my grill already, there is no way you could squeeze a winch like that under the radiator like you would like to do (like a smaller planetary winch).
There really isn't anything wrong with the planetary design and if you are looking for a hidden winch its pretty much your only option. IMO big companies like Warn switched to planetary winches because Jeeps have trouble fitting bigger winches and cooling problems can develop. There is no question that Jeeps are their biggest market.
Of course, having a winch that's smaller and lighter never hurts
If you haven't guessed by now I have a Warn 8274 on the front of my truck (it hasn't left the truck since it was bought by my father in '83). It has performed flawlessly for almost 25 years.
By the same right, my brother has a Warn XP9500 and it seems like a great winch too. Pulls hard, compact design, reasonable price (the newer 8274-50's are too expensive IMO).
So....
Since you want to hide your winch, you need a planetary winch. It seems you don't want to spend tons of money so IMO one of
T-MAX's winches are the best option. They are technically Chinese made but are much better quality than the others (run far, far away from Milemarker winches)