I won't consume my time in explaining the difference, since it has been debated a lot of times in other forums as well.

All I would say, EE versions, specifically BG2 isn't worth at all rather, it's the same game, with better graphics (to an extent), modern PCs can play it smoothly and with extra companions (and these suck, not at all interesting) and content (making game too easy).

The good thing about BG2EE are improved enemy AI (much tougher than vanilla), new Kits, some rule changes, and improved UI.
BUT, by merely looking at the bugs, there are however present and will require few patches to be at par with the"GOG BG2 version + BG2 fixpacks + BG2 tweak pack" game.

The only EE worth purchasing is the BG:EE and that's a relief to play on modern PC's since GOG BG with BGT and other mods still create problems on the modern systems.
The BG:EE also looks great compared to GOG BG version.

So, I would say skip BG2:EE but try BG:EE.