I will preface this with a, "in my humble opinion"... 
I would say either wait and go for Captive bred ornates when you CAN afford them, or get the malis. The malis may be less colorful but they are wonderful pets, and get a bit bigger I think than the ornates, though that may not be a fact.
The wild caughts will often cost you much more in the long run due to vet fees, time, and heartache. I do not know your herp background, but I feel that 1) the importation of these species should no longer be supported and 2) that wild caught specimens should be left to the very experienced Uromastyx owner/breeder so that they have the best possible chance for survival.
Speaking to the specific, "ornate vs. mali" question, I don't think you can really lose, they both seem to be winners! In general it seems like the ornates are a bit shyer and more sensitive, but that is just from reading the board posts, I do not own an ornate, just a mali and an Egyptian.
I hope that helps a little!
Elizabeth
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1.0 Mali Uro Archimedes
0.0.1 Egyptian Uro Zuberi Mosca Khu (Mosca)
0.0 Fish
0.1 Sulcata Minnie
1.1 Iguanas Flik and Loki
0.1 Newfoundland Jasmine
0.1 Feline Winter
Indiana & Wisconsin