I'd have to say that because there is such a debate, there's no best; it's all based on your playing style:
Kol:
- Best hp and armor
- Flak bust for anti-fighter defense; gauss gun for single targets
- Finest hour is a really nice ability; considerably raises firepower, rate of fire, and regenerates anti-matter
- Adaptive forcefield for defense
Radiance
- Highest shields, weakest armor
- Animosity useful, as Advent ships tend to be weaker and more fragile
- Detonate anti-matter can be very useful against anything with anti-matter, including other capital ships
- Final ability, Cleansing Brilliance is an awesome ability; very good vs capital ships and any supporting targets nearby
Kortul
- Most weapons are designed to face the front
- Power surge is useful for engaging both enemy fleets and enemy capitals (especially at level 3)
- Disarmament is good for taking out enemy strike craft (keep Sentinnels nearby to support the vessel)
- Disruptive strikes I think is useful in that it slows down cooldown, but not so good for anti-matter depletion (too slow)
- Nanites is also good as a multi-use vessel
All in all, I'm not sure which one is best. If you're talking about who would win at say, level 10 with a pair of bombers, well, I would actually have to lean in favor of the Kortul, although I'd need a test to see. You see, the weapons on the Kortul are forward facing, so that makes it more likely to win.
Could somebody test the following in controlled conditions:
- Kol vs Radiance (both lvl 10)
- Kol vs Kortul (both lvl 10)
- Radiance vs Kortul (both lvl 10)