A pair of Aces among your hole cards is a very good starting hand in Omaha. Even so, it is nothing like such a powerful holding as it is in Hold'em.
In Omaha the pair of Aces represents only half of your pre-flop holding. The other two cards are also important. A pair of Kings would be a very good accompaniment to your Aces, as would a Jack and Ten to offer good possibilities of making a straight. Ideally both of these hands would be 'double-suited' to allow chances of a flush, i.e. A-A-K-K or A-A-J-10.
There are lots of mediocre holdings in Omaha, but very few really terrible ones. However, it is never desirable to have three or four of a kind in your hole cards. You can only use two of these cards, so there will be some redundancy in your cards. Furthermore, one of the cards that you would like to see on the board is in your own hand! Thus the worst starting holding in Omaha is four Deuces.