Definitely Adom style. In Adom it worked very good, and I'm used to them. But second dungeon style also doesn't look bad, if in JADE dungeons level would be in different styles(some like in Adom, some like second dungeon from your post, and some others) it also could be fine. Only thing I really wouldn't like to see in Jade are multiscreen dungeons levels(like in Angband).
I like old ADOM style more. It's more entertaining. It's mysterious
RPG dungeon with doors, traps and lairs. Of course there
could and should be some natural caves but I hope most dungeons are classic RPG dungeons built by ancient people and designed for epic adventures ;)
Personally, I'd love multiscreen dungeons - or at least dungeons larger than ADOM's 80x25. Double that size (80x50) would easily fit on one screen nowadays.
While multiscreen dungeons would get annoying if they were too common, imagine a new version of Infinite dungeon where first floor would be, say, 10x10, second floor 11x11, third floor 12x12... etc, without limit.
On the topic of multiscreen dungeon levels: Incursion has them, with the option to keep your @ centered in the middle of the screen (and the dungeon basically scrolling around you) so that you don't have annoying 'leaps' from one screen to the next. And to keep an overview of the level it has a zoom view system which works suprisingly well, even in pure ASCII.
It also has both types of dungeon proposed above (and a few more) integrated into those big levels.
I think it should depend on the dungeon in question -- is it a wild cave system that you're spelunking, ancient ruins, caves that have been converted into living quarters by subterranean races -- all should have differing layout styles.
"The map generation code is completely pluggable so that over time there will be different map generation algorithms especially for dungeons. Right now there are maze and standard dungeon generators and a multitude of generators for various city/town/village layouts. More are to come."
So hopefully JADE will be very rich in numerous map dungeon types. I also hope for multiscreen dungeons, with the ability to centre the view on the character. What I'd really like to see is more random dungeon features - structured temples filled with priests, containing an altar and a few magical items and books; barracks filled with soldiers of a specific race and some leaders, with a cache of weapons and armour; random small towns of orcs or other creatures, who may or may not be hostile (and a good character would have to think twice before fighting back against the group of orc children, or slaughtering their parents in front of them). There's a lot more possibilities for random features.