Hmm. Probably the Scarab. It's a surprisingly fragile ship, despite ostensibly decent armor and high hull, and due to the nature of the Temporal Shell, it's easy to get carried away and caught out. The are also more-pronounced-than-usual choices to be made when deciding how to fit it, especially in terms of whether to leave some slots empty. For all that, the Temporal Shell gives it some unique tactical opportunities.
I'm not entirely sure how powerful it is, to be honest. Which is why I'd say it's one I'm most pleased with - I think there's a good deal about it to figure out. (And perhaps tweak, later!)