Best leveling Co op protoss commander?

Just finished getting p3 artanis to lvl 15 again.

Looking for new rewarding protoss commander to lvl up. Should i go karax, fenix or zeratul? My friend does alarak.

So far i have started on fenix, but he does not seem rewarding below lvl 10 to lvl. Can i utilize his prestiges while working on getting p3+re15. Should i swap commander?

Any tips on late game artanis would be great. I feel like i can never build a final army with him, tend to be the field and orbital support guy, curious if the potential goes past that.