For me as the name implies I really dig the Miranda class vessels. The Wrath of Khan was my first experience of Star Trek and I loved it. The Connie was the hero ship and fantastic but the Reliant seemed rugged and compact and the fact it went toe to toe with the flagship says something about it. Later usages of the ship also implied it as being a tough little ship - outfitted as the Souyez class etc and serving on the border etc.
But these two designs the Connie and Miranda have inspired much of the rest - The Galaxy and Nebula borne of them for example. But also like the Intrepid class and the Akira. Would love to have seen it on telly or featured more on the big screen. Really cool and powerful but seems rather practical in its function.
Of course as mentioned the Romulan's Big Green D'Bird - unfortunate that its sheer scale and size was often not conveyed on the screen. One wicked enemy to come against. Shinzon's new ship had nothing on it for meaness and impressing the enemy facing it.
The Klingon bird of prey is also one swoopy mean fighter too - Dominion war showed it kicking ass [though by the same token the DW horribly maligned the reputation of the Miranda sob]