I have a lot of moments that could qualify as best MWO moment in my Splatcat when splatcats were all the rage. One match (when it was 8v8) in River City Night I basically just went behind their team, and 1-2 shot everyone they had because they were distracted by the rest of my team. With an atlas getting 2 shotted, and he ran away and was the last one alive (He had no arms/side torsos left), I didn't finish him off because while splatcat is awesome, it is a tad low on ammo so you don't want to waste any shot It was like playing the Spy in TF2.
Just any game with Catapults(excluding K2, which removes 2 things that makes the catapult awesome) is a fun time though. Perfect blend of everything, and I love missles.
More recently, a less than a week ago I had a duel in a Wolverine 6R vs a Highlander. He and his buddies were going straight for our base on assault, however his 2 buddies ditched him, and I was standing behind him for a couple minutes so I could spot for an ally because we had some LRMers. He got close to seeing me 2-3 times making me go "OH ****", since while he was built more for LRMing, he actually had some decent backup weapons, and I'd rather not let myself get hurt more than I need to. When he finally did See me, my ally stopped firing LRMs on him soon after that (probably to kill the Assaults killing the base). So I had an ice long duel with the highlander, then I almost finished him, but I ran out of ammo on my LB10x (I killed TimberWolf that was harassing an ally earlier, and shot some other people too), so I lost more of my damage that way, so he then killed me when he had a cherry red torso. Less than 3 seconds later a Spider comes by and uses 2 medium lasers to 1 shot the highlander.
Another good one is where a cataphract buddy (not grouped mind you, I only pug) and I basically defended our base on assault (before turrets were added) from 6 different people, just long enough for our team to steamroll the rest of their team, and come back to the base. My memory is a little fuzzy atm (and I'm too lazy to search my own post for the specifics). Though I will say, seeing nearly full health allies come back to your base to finish off some enemies that are almost dead when you're almost dead makes you go "OMG THANK YOU! HELP ME!" even when there were only 2 very injured enemies left.
Another fun game was where my team got heavily steamrolled when I went off to cap gamma in Alpine peaks. Then I asked the enemy team for a duel at gamma since there was no way I would win against 10 people. Only a hunchback came, so I proceeded to duel the hunchback, He killed me, but I missed a couple shots which led to my downfall when he only had 1 hit left. It was a good duel. This was when I was still rather new to MWO, and during the very short time I played a dragon (playing it later when CW comes for reduced cost/whatever benefits). I may have been a heavy, but when the only weapons I had on me was an LB10x, and a couple medium lasers, against Laserboating Hunchback on a cold map, I can't say I'm too surprised he won. We had a little fun chatting after.
Getting into mediums lately because of queue times, and because I know I'd rather pilot any other class other than mediums, so I'm getting them out of the way, and so I don't diss the class without playing it.
Anytime I kill something much larger than myself by myself feels really awesome, I just don't get that whenever I pilot a heavy because you're rather expected to do that because of all the damage you dish out, while still having similar speed to a medium, and having more armor.
Playing the Blackjack today for the first time, I feel as if I have invisibility turned on or something, everyone always ignores me to go kill something else. It also takes them much longer to realize I'm there when I'm shooting them when I'm hill humping, even when they were looking in my general direction in the first place. So because of this, I've gotten a lot of really easy kills with the Blackjack. Makes me feel like I'm playing the spy from TF2 all over again, I just keep getting up behind people and nibbling at their rear armor.
In a recent game I was being an absolute tard on crimson straight by jumping in the middle of 7 enemies, and I never got shot once (intentionally anyways). They were all distracted from my team shooting them from all sides, but it was surprising none-the-less because you'd think at least one person would change their focus towards the blackjack that just shredded a Dire Wolf's CT, then killed a Wolverine by shooting it's rear. The whole time I wasn't even making an attempt to dodge anything aside from a little back and forth motion because I was being lazy.
There's just something so awesome when every mech in a match is at the same place all firing at each other at the same time, with you being in the middle of it all, and all it takes for you to die is just for someone to look in your direction and shoot you in the back once or twice.