You could always use more A/D =3
That does seem to be one of the more popular game modes.
I personally like the idea that the map doesn't have to be symmetrical, symmetry in a map kinda ruins it for me.
Also, you should specify CAPTURE POINT A/D, because technically Payload is also a form of attack/defend, if not the way we know it (and I think it should specifically be capture point A/D, because if we include payload as an a/d option, it will become a gamemode-popularity contest instead of a mapping contest)
Also consider narrowing down which possibly attack/defend variants are open for use, because just like with payload, inclusion may turn it into a popularity contest of gamemodes, not maps.
Total options are...
MSCP
SSCP
A+B=C OR variants (A+B+C=D, etc.)
Assisted Control Points (like Steel, where you have one specific goal with helpful additions)
Misc/Other
(did I miss anything?)
I'm worried about MSCP in general, but I already voiced that concern elsewhere.
It would be feasible to group SSCP with A+B=C (and variants), as well as grouping Assisted Control Points with Misc/Other. Those at least seem to me like the best groupings, if we were going to do a generic "A/D Control Point" contest.