[holden]

Hi and welcome!
You're bound to get a bunch of opinions on which is the "best" Underworld album - they all have their high points, but i dunno if there's a definitive record.
As an introduction to various parts of their career, maybe check out their compilation "Underworld 1992-2002", a 2-CD.
Or, to prep you for the live experience, get "Everything,Everything", the live album from 1999. Sure, they have two more receond studio records since then, and lots of newer tracks, but you'll get a great impression of the improvization, energy and mixing of the live show.