This is quite hard to decide, methinks. I'm must admit, I'm a 'bigger is better' type of person (at least with regards to capships!), but each faction has their own style.
Of course, the Kilrathi have the longest capship known in the WCU (AFAIK), but I think, for the most part, Confed and Kilrathi had similar design philosophies. ie corvettes, destroyers, frigates, cruisers, carriers, etc were all alike in function and design, according to the respective species' style (at least in WC3).
Nephilim ships are slightly different - and massive, at least with what we have to compare with regular WCU capships. They seem to have a 7-point design philosophy, but other than that, are analogous to the Confed and Kilrathi ships (barring the Kraken ship killer, of course).
I think it might be interesting to know what sort of capships the Steltek would have used. Someone made a 'Mediator'-class carrier based (I assume) on the derelict base in Delta Prime. Looked quite devastating, especially given the Steltek's technological superiority. Fortunately, they don't seem inclined to use so much force (at least for the moment).
I'm rambling, these are just my (spur-of-the-moment) thoughts.