Go brushed unless you're very serious about rock crawling. Brushed motors are much cheaper and perform very well considering rock crawlers are only designed to go slowly.
Most rock crawlers have brushed motors as they have great low-end torque/control unlike sensorless brushless motors. If you are wanting to step it up to brushless, just make sure you get a sensored brushless setup.
Here are a few things that you should think about when buying an RC car for someone else.
Tip: Unless they've specifically asked or expressed interest in on-road RC cars, off-road vehicles are a safer bet as they are more versatile as they can drive on the road and off-road.
RC rock crawlers don't go very fast so you tend to break a lot less compared to a high-performance RC truck. Most breakages for RC rock crawlers are typically around the steering system (tons of dry steering) and the drivetrain and they are under the most load. However, regardless of how strong the RC car is, it's a matter of when it will break, not if it will break. That's why parts support is essential - we stock parts for all the cars we sell so you can purchase your RC car with confidence that we'll have your back when you crash into that tree that came out of nowhere!
The answer to this question is very subjective as it's difficult to measure the 'durability' of an RC car.
Electric: Most electric RC cars are waterproof* - just double check in the description of the RC car you're looking at.
Fuel powered: As all fuel powered engines need air to operate there's no truly 'waterproof' fuel powered RC cars, however, there's some that have waterproof electronics which essentially makes the car 'splash proof' - never submerge a fuel powered RC car.
*Note: if you drive in water (especially salt water) make sure you clean it thouroughly. Driving in wet conditions will increase the wear and tear on components such as bearings, tyres (they can fill up with water and overload your electrics and damage the foam inserts) and various metal parts. Even if your car's electronics are waterproof, it's best to stay away from water.