In any case, it is better for beginners to start with hold'em, because, to put it somewhat simplistically, Omaha is the same hold'em, only with four cards and with a large number of combinations. Well, anyway, in hold'em in live tournaments and in kilofields, the lineups will always be better, the player's expectation will be higher than in Omaha.
The cash game, of course, is somewhat different, but I repeat about the base: the ability to play hold'em is a necessary basis for Omaha.