I always prefer Competitve Custom Games over MM in General. Sure sometimes when you don’t have enough people to get a full lobby of 16 people and your stuck with MM but I’ll always go with Competitve Customs since the games are always close and everyone has a microphone. It gets boring sometimes going in as a group in MM against other people. Edit could a Mod move this to the Xbox MCC Forum?
I wish they offered better party up functionality after a matchmaking game. Also an indicator in the game lobby of who is partied up together would help. If you normally run solo but see so many others in a party, it will encourage you level up and get with the communication
Customs are good for practicing specific game types that you need work on. MM is good for variation on who you are playing and the game types. Both have good results.