Much as some here clearly don't like corridor connections, even they know that through gangways are important in some cases, so couldn't we have examples of both from posters?
For example, I think that the 350/444/450 Desiros are quite acceptable implementations of a gangwayed front but the 380 isn't. The 172/375/377/379 Electrostar fronts are also fine.
For non through-gangwayed stock, the Desiro 185/360 fronts are OK as are the 170/357 designs. The 376 & 378 fronts don't look so good, but like the 319, the 378 has to meet both signal sighting requirements yet have emergency egress in tunnels so the aesthetics of the design are compromised.
One thing that I think does create poor results is when original designs are modified away from their original design team. The MKIII MUs are quite respectable for their time, but attempts to add/remove gangway connections spoil the lines of the original design as seen in the 455/8 modifications done for Southern. I think that the original 455/8 (and 317/1) design has shades of US railcar design and does not look out of place.
Going back further, as has been mentioned above, the 309s with their original curved windows were smart at the time, as were the 124s and 303s.
SR Nelsons, 503s and early non-SR DC stock as found on MS&JR and Watford DC lines.