I haven't used them all so I can't really say which is the best. With stocks I try to use 5% margin for all my trades. If this amount of leverage isn't available with MQ Prime it's almost certainly available with CMC. I also keep CMC active because MQ Prime won't let you short any Macquarie products. I've seen an independent online comparison/review between most of the big providers recently, but I'll be stuffed if I can find it again. It was very informative.
