I'd say try both for a couple of hours, or if you MUST choose 1, this one. Reasons for that:
1 - Nergal's 1.1 has a reworked and finished story: Personally I like that now every character is fleshed out (pun intended) and feels at least a bit distinct from the rest. A couple loose ends here and there but every important character is there and you see a lot of them. The modded version merges the old story with the continuation of the new one (from 0.8 onwards I think). And if you DON'T care about the story, you can choose a fast progression mode, which leads to my next reason.
2 - No grind: The original UD had a 3-part point system that you needed to complete in order to advance ( Purity/Corroption and Hearts). At best it was grindy and at worst you HAD to check a guide to see what the hell you should do next and when.
The modded version still uses this system, while you can totally mess with the point values and other variables, you'll probably need that guide anyways.
THIS version has NO grind. It works a lot like a Light Novel: go somewhere, do something, make a choice (depending on your path), get a scene, repeat until the end. You do all of this with a guide ALREADY INCLUDED in-game, just check your Phone Diary and you're set. And like previously mentioned, you can speed up the process with a Fast Progression option (I haven't tried it, though).
3 - Plenty of content already: While there was some content that didn't get made (beach scenes, car wash scenes and pool shower scenes), this game still has a lot of content. Be it story or animated scenes, at present it's nergal's longest game. Now the modded version DOES have a LOT more scenes, BUT keep in mind that most of them are re-used scenes from the original but with different characters (for example the Mom has almost every scene of other characters as hers). There are some good originals, or the story around those re-used scenes, so do check it out if you still want more content by the end of UD.
Regarding bugs and crashes, I haven't encountered a game breaking bug in 1.1, and anything I did encounter was solved reloading a save (save often in both versions). Also I only got 1 crash, but I always get at least that in a RPGM game. So I'll say it again, save often.
