KoTH is the best mode.
It's the fairest, equally balanced since both sides are required to be Offense & Defense to win the round. Rewards adaption and teamwork.
Offense on Cap/Payload is the most braindead and probably highest win-rate mode. There's no way to "wander", so Offense can eventually get a push sync'd even by accident. Also can end rounds early by getting off 1 good push and capping which avoids dumb mistakes as the round drags on.
Being a Defender is worst, no matter if payload or capture points. Ease of players to wander around and leave the objective site are too high. Requires more teamwork and for longer duration. Easy to have a misplay since you're required to defend for so long.
I've narrowed down my SoloQ woes to having to be Defense as 1st game, practically always. New Strat is to dodge my 1st game if it's a defense round. After 1st game you get settled in with a team and also benefit from Consecutive Round XP, but as 1st game of the session I'm avoiding Defense now.