In-game... have yet to fly it, but on looks alone, the Imperial Clipper. Of the ones I have flown, I'm rather partial to the Cobra for functionality.
Out-of-game... the carriers from Thorarinn Gunnarsson's Starwolves series of novels (circa 1988, fluffy sci-fi, not particularly great storytelling, but interesting universe). No picture of them exists; rough description... 3km long, roughly arrowhead-shaped; two sets of 4 drives, one set pointed backwards and one pointed forwards for braking. Heavily armoured and armed, main cannon could destroy a world, carries 400-some fighters. Extremely maneuverable, could stop on a dime, though this involves accelerations that only its alien crew could handle (but not humans). Built to last, most of the ships are thousands of years old, though their number are few (only 22 exist). But most importantly (and amusingly), a sentient AI running the ship, which tends to be on the eccentric side.
(Anybody else read this series before? It seems to be rather obscure... I picked it up in the library way back when on a whim...)
I named my Asp the Valcyr, after the one carrier that due to a runaway experimental jump drive, made an accidental exploration of another galaxy and had to limp home (having lost her crew

), and then parked herself inside a glacier on an abandoned Earth and brooded for the next few ten thousand years, not knowing what happened to everyone...