My favourite is Kalos. It's the most interesting to walk though, actually has decent pokémon to battle against if you just want to level up, and doesn't insist on you using obnoxious HMs (Hoenn's Victory Road and Flash >_> ). Oh, and the music was awesome
I liked BW's mostly because of the gates before the cliffs themselves; the buildup effect on the music was magnificent, especially once it all came together in a crescendo once you stepped into the actual Victory Road area, with the cliffs and all. It was a surprising sight, since I was expecting another cave as per tradition, and it's left a good memory with me. Only complaint: every wild battle is the spazzed-out version used for shaky grass encounters. Just a bit overdone there. Otherwise, it's a good atmosphere for the situation: ascending a steep mountain to your final goal.
Kalos' broke the mold by both looking beautiful and not being composed entirely of cave maze, but it didn't leave the same "holy crud" feeling I got from the original Unova's. Also, I was disappointed by the removal off the buildup music at the gates in BW2. That was the best part!
I don't really have a favorite Victory Road, but I find the ones in generations V and VI to be unique in comparision to the other ones, which feel too aesthetically similar imo. On a related note, I don't remember Johto's very well. Part of it is probably because I haven't been to that region in quite some time, but part of it is because I didn't find myself there for very long compared to all of the other ones, thus it didn't leave me with a lasting impression. As a result, gen. II's Victory Road is my least favorite, while I like gens. V and VI's the most.
Black & White's Victory Road is more memorable than the one from Sinnoh and Kanto/Johto which was just a generic cave filled with tough Pokémon and ''elite'' Trainers. Fighting all those Durant with Moltres is surely more memorable.
I actually hate Victory Road, it's too long and annoying.
However I found the Kalos one actually enjoyable because it had good design and wasn't so boring as a damn tunnel. I do like BW2's victory road's design but not quite as much.
Old Unova Victory Road: Its got music fitting for you trying to reach a summit. Its also got a funny scene involving an Ace Trainer wimping out from sliding down a cliff. The road itself also actually looked like a climb, and much less a generic tunnel route.
Kalos: Even better music and a vastly superior scenery involving a mountain on top, and a cliff overlooking the land below. Add the thrill of wild Pokémon swooping down on you (holy £@€¥!!!), and you've got a Victory Road that is anything BUT boring.
I voted for Kalos because aesthetically it was simply amazing. It had the perilous caves, it had outdoor locations, it had ancient ruins(!!) it was just downright perfect.
Unova's Victory Road in BW2 was also great, again because of the outdoor sections breaking from the monotony of cave routes, and also because of the ruins of N's Castle(!!!) showing you tangible proof of the events of BW.
I also have to give a shoutout to Gen II's Victory Road. It was understated, but the way there were no trainers in the cave actually helped to build a sense of dread. I think Silver comments on how the Road is so desolate because nobody had the guts/strength/skill to make it that far. It makes you feel accomplished for continuing it. Although I suppose it could be argued that Routes 26/27 were the stand-in's for the traditional trainer filled road. In which case, Johto broke away from the 'cave tunnel' mold before it was cool.
Unova's in Black and White. It really felt like that was the end of the game. The music of Route 10 leading to Victory Road is one of my favorite tracks, and Victory Road itself felt jagged and rough, like it could break you at any moment. Absolutely loved it! Black and White 2's Victory Road wasn't anything special and I would go as far to say that it was really forgettable.
Kalo's comes in at a close second because the scenery was gorgeous and the music was very fitting!
While I did find Gen II's Victory Road memorable, I remember it for the wrong reasons. It really felt empty and a once populated cave with trainers is nothing more than an empty shell. The music didn't help the mood. It felt really depressing.