I play a bit of Omaha.......really prefer omaha hi/lo myself but still learning both.
I got ahold of Lou Kreiger's book "The Poker Player's Bible" and it shows that there are 41 Very Best Omaha hands.........not going to list them all I would be here all day typing this but the utmost hand is AAKK double suited and the lower end of the scale is QJT9 rainbow.
Aces and faces double suited are what you want but in the midst of these hands paint pairs and 2 other faces work out well also. In Omaha and hi/lo preflop raising can go to extremes. I haven't played a buyin tourney yet on these I play mostly freerolls
on these 2 games since I am still leaning alot and I have seen more than person go all in preflop with a great starting hand only to burnout by the river.
Unplayable hands example:KQ76 rainbow. You wouldn't want to bet out of position with this hand(maybe catch a flop in the blinds) But most likely would lose to a flush or a boat. Another example of worst case scenario hand is QJ65 double suited. Looks good but more than likely get you into trouble.
Double Small pairs like 4433 can produce low sets and baby str8ts that will cost you alot more than you are apt to win if you get "lucky"
7s7c4c2d: All your possibilities are weak. A set of sevens is no guarantee of winning the pot. Making a seven-high flush or a str8t using your four-deuce or seven-four combo will produce hands that can easily be bested by others.
Like I said before I am still learning and I think I like Omaha 8b myself better than Omaha. Now that's a way different game and stratedgy than Omaha I hope I was some help to you.