I used the free version for a long time. Just checked and now I'm on the paid version but don't remember why. Mostly I just use it to follow my son and keep up with his high school track workouts. My rides go on there automatically but it's rare that I actively do anything with it.
Strava for mountain biking seems like overkill. Every trail and type of terrain is so different that keeping track of mileage really doesn't mean anything like it does for a roadie or a runner. 10 miles on one trail might be a casual cruise while 10 miles on another trail might be a multi-hour ass-kicking. I guess a lot of people use it to chase KOMs or to compare their efforts on a trail. I'm rarely ever aware of how fast I go or how long a trail takes me. I tend to judge myself on the obstacles I clean or fail to clean each ride without regard to the speed.
Trailforks is my go-to app. I use it to find trails, to get un-lost, to remind myself of trail names, etc... MTB Project is also good and has better descriptions of trails if you're somewhere unfamiliar, but for just seeing them and navigating them I like Trailforks user-experience best.