The truth: You need at least one of each (you could skip out on the carrier if you have a large fleet)
However, I feel that the Marza is the only capital ship that under performs, its fire power is relatively close (slightly better) to the Kol's but with a lot less survivability and when you're fighting either AI zerg or anything else for that matter living by a good margin is a lot more important than dealing the extra 100-200 damage.
If I am going for a cap ship build, it's generally : Kol , Kol , Support (the one with shield restore)
Carriers are pretty good (arguably better than everyone else's?) but you need them in packs to be really effective without support. If you have support chances are a Kol would still be better.
You want to most likely start off with a Kol because you're going to be fighting multiple encounters and god forbid you run into a planet guarded by flak militia which will dampen your carriers. You also want good dps/armor with self-sufficient abilities and that weeds out the support ship with the shield restore/emp. So, that leaves the Marza, Kol, and Akkan's.
Akkans might actually come close to the Kol because you may be able to colonize faster but you won't be doing much in the ways of harassment/damage and the other abilities (ion cannon / passive range/hit buff) do not make it a heavy hitter unless the 5% hit and range increase actually does more than what it says it does. That being said, the Akkans still has low armor and less hull/shielding which leads to a faster death.
So that leaves the Kol and the Marza. Marza is out because while it does good damage, it has crap for survivability and it seems (I am pretty sure it is) a lot slower.
Anti matter abilities early on aren't that great because you spend a lot of it phase jumping around.
I am not really sure if I can justify using a Marza even with a 16 fleet cap armada simply because I am expecting mass focus fire and the damage out put isn't serverely more than a Kol. You'll want as many of your cap ships to survive a massive encounter as possible thus most of your fleet will be taken by the Dunov / Kol with one or two Akkans for the passive buff. The rest of your fleet would be repair ships, kodiak cruisers, flak frigates, and all your flights are loaded with bombers. Most of your damage won't be from capital ships , their job is to survive provide extra support for your Kodiaks / whatevers. They also require the most grooming of your entire fleet so survivability is a must otherwise you can kiss that 3k credit 400 metal 300 crystal + time in experience good bye.