The UK version has all of the main episodes including the following:
■ Special Bonus Episode "Kuro Runs Away From Home"
■ Ura-Eku (short comedy video) - Part 1 and Part 2
■ Web version Previews - Part 1 and Part 2
■ Commercials and Trailers
■ Textless Opening and Ending - Part 1 and Part 2
The US version exclusively gets these:
Box Set I:
■ Blue Exorcist Original Soundtrack CD1
■ Bonus DVD: English Cast Interview Part 1: Okumura Brothers & Cram School Gang
■ 36-page Deluxe Illustration Booklet I
■ Rigid Box illustrated by Manga Author, Kazue Kato
■ Clear BD Cases with 2-sided Japanese Cover Design
Box Set II:
■ Blue Exorcist Original Soundtrack CD2
■ Bonus DVD: English Cast Interview Part 2: Exorcists & Demons
■ 36-page Deluxe Illustration Booklet II
■ Rigid Box illustrated by Manga Author, Kazue Kato
■ Clear BD Cases with 2-sided Japanese Cover Design
Basically on-disc wise you'll have all of it no matter which version you chose but for the usual AoA stuff you won't get those.