Just keeping it to best buddy so you’d have to actively consider your team and could at most have 1 pokemon with 3 moves as well as whether getting that 3rd move in masters classicis worth giving up Dialga’s break point.
What would you like to 3 move in each league.
Great: I was tempted to say Azumaril, Hypno, but settled on Jellicant.
((Mew would also be tempting but unfortantly because I chose Best Buddy to limit it to 1, mine would be ineligible if BBed)
Ultra: I thought about Scizor but settled on TinaO
ML Classic: I thought about Groudon, and Machamp but Mew2 (IB/FB/Strike) though I might stick with Dialga.
ML… I dont know I dont play it :>
Anyway, just for fun speculation