Forgetting the numbers and going with my impressions, the smallest just doesn't look formidable. It looks cute. A small personnel shuttle limited to one solar system. A transport. A gad fly. A sitting duck. I can't take it seriously.
The third one, "large", looks ungainly instead of threatening. Which doesn't make much sense, really, as they're all the same shape. So what makes this one more ungainly than any other?
The second one, "medium", looks sleek and capable. If I were to choose one for a stealth ship by its looks alone, this is the one I'd choose.
But the forth one... XL... It looks Romulan to me. I know that doesn't make sense but there it is.