I think I heard this on the barry greenstein ace on the river audio book, but he was talking about where the best games of each genre reside (hold em, stud, omaha). He was saying this from a standpoint of if you want to test your self or better yourself this is where you want to go.
I can't remember the exact locations of where he said the best hold em and stud players reside, none of the locations did he mention more than once, but I remember everything he said I was agreeing with/thinking that it made sense. He said go to Europe for the best omaha games/competition. Now obviously you don't want to purposely play the best, you want to play fish if you have a choice, but from an experience stand point it damn sure helps playing the best.
I agree with Greenstein on this one that the best omaha players reside in Europe. What separates the European omaha players to the American players, is postflop play, I think the European omaha players postflop play is much better generally. What I think the Americans are best at in omaha is calculating outs to win on the flop, playing the percentage game, and understanding what hands are good preflop and playing for only the nuts. Theres only one problem with this tho, when you play 6 max and damn near seemingly every hand is raised if you play for only the nuts you'll get bluffed off of winning hands alot. European players are definitely good at floating and
bluffing every scare card in almost all situations, a risk alot of American players don't really take as often that works pretty often when you push it.
at the end of the day, in omaha, I think postflop play is more important than math in omaha just barely. Europlayers don't focus on the math as much, but don't get it twisted some of them definitely do and the ones that do that
bluff alot are VERY hard to deal with whether its hi/lo or hi.
so all that math and those books will help, but I say you play with some american players to get your math right, and play with some euro players to get your postflop play right. Europlayers will also help you get your preflop game better too in omaha. US players don't reraise often enough WITHOUT ACES. Its too many situations where people are raising every single hand, and people get comfortable calling when you should be widening your reraise range BIG TIME. For the most part, throughout my experiences in PLO and PLO hi/lo the best players are the ones that are selectively super aggressive, I know that sounds stupid, but yeah, selectively super aggressive. There very near hypermaniac aggressive, but they know when to slow down, but they have a real good feel when they can get way with leaning on you non stop once they know how you play.
I havent really looked into too many omaha books, I got my omaha start from super system 2 and that gave me general idea math wise and you definitely need to understand the math. But Its some postflop concepts that I just assume isn't really taught in books, I would say if you could find a book that goes in depth about postflop play, bluffing, betting, raising preflop, reraising preflop, and raising reraises preflop (without aces, probably sounds crazy but definitely happens when stacks are deep), redraws, etc. I don't think any book is going to tell you how to raise, have someone raise you, than you reraises that person again pot max without aces in deep stacks. I'd be surprised if a book goes in depth into postflop play on omaha outside of the math side. Good luck in your book search, once you get past the math aspect, nothing will be better than experience though.