87 and Mk3s
Class 442
HST
91 and Mk4s
Of the first two, I'd say 87s are non descript looking and when paired with a MK3 DVT looked hopelessly mismatched.
Class 442s i would consider to be pig ugly (pun intended). Stock with corridor connectors rarely look good, but 442s fell out of the ugly tree and hit every branch on the way down. I would pay a small fortune to wield the cutters torch to a 442.
HSTs, a genuine design classic and aesthetically very pleasing, but should be pensioned off now. I think they're probably the most attractive train on uk metals since ww2, but they've had their day for frontline service.
Class 91s lopked amazing when they were introduced but to me seem very much of their era, but not quite old enough oigh to have a retro charm about them.
Goes to show beauty is on the eye of the beholder and all that. I like 47s.
The 37s and Deltics and other eary diesels look to me like scaled down American locos to me and look crude and ugly, but without the size and scale of their American cousins to generate a sense of awe.
In my opinion 47s have a more European/British design to them and made their contemporaries look dated.
I also like Network Raik's Ultra 73, one all the bagpipes were removed, it gave the loco a fresh clean look that I'd been oblivious to all these years, like the dowdy librarian who takes off her glasses and ahakes out the bun in her hair to reveal a ravishing beauty.