Played baseball from 7-15. It is boring, but I was a catcher so I kept busy talking shit to the hitters. Not very physically demanding apart from beating the hell out of my knees as I grew.
Played football from 12-21. Midget and high school football (I played LB/FB) were fun. College (I played LB) was a fucking grind. Recovering from a game usually took 2-4 days depending on what part of the season I was in. It was really not that difficult physically (probably because I knew how to prepare for it), but it beat me up really bad.
College football was also very challenging mentally. Offenses were complex, our defensive scheme was complex to match, and I wasn’t very talented physically so I had to do a lot of film study to be worth a shit. I’d estimate that college football took up around 25-30 hours/week of my time in season. Average of 2 hours practice/day, 5 days a week plus an hour meeting each day, then another 90 minutes of film on those days. Game days were probably about 8 hours in total from pre-game walk through and meetings, to warm ups, game, post game, etc.
Wrestled senior year of high school. Much harder than football physically. It is also much easier to recover from a 6 minute match against someone your own size versus a 60 minute game slamming into people that might outweigh you by 100 lbs or more. I would feel fine the day after a match, whereas the day after a game I’d feel like I got run over by a semi. The mental aspect of wrestling was non-existent. Once you got the feel for the mat, everything else just came together on its own in practice.
Fought MMA a few times before senior year of college football, then trained it again after school for a while until I effed myself up (skiing) to where I can’t roll anymore. MMA is the hardest thing I’ve ever done physically. Three 5 minute rounds is brutal, especially if you’re a lighter heavyweight (210-220) like I was.
After my second fight, which went the distance (I lost after gassing hard in the second round), I puked/gagged for 5 minutes straight and couldn’t catch my breath for about a half hour. I didn’t really understand the conditioning aspect of it until then, because I won my first fight in 50 seconds. I was not prepared for a 15 minute fight. I also had a tough time relaxing and dealing with the adrenaline.
The next day I felt pretty much fine. I didn’t take any hard body shots or leg kicks though, just got punched in the head a lot.
So MMA is the hardest, conditioning-wise, and football beats you up more. Football is also much more difficult mentally. MMA (for me, with limited training) was just reacting. I didn’t even have a game plan outside of beating the other guy up.
Wrestling is like MMA-lite. The periods are shorter and you don’t get punched/kicked, so it’s easier to relax and not burn yourself out early on adrenaline. It’s still hard as hell, just not harder than MMA.
EDIT: I’ve competed in powerlifting a few times in the last few years. It’s fun, and not nearly as challenging as any of the other things I’ve done, baseball included.