Having used both for a decent amount of time, I can tell you there isn't much difference in PERFORMANCE between the 2 machines. They both offer about the same analysis of the target and about the same depth. The real difference is a lack of a pinpoint feature on the Ace 150. This isn't too big of a deal if you have a handheld pinpointer.
I will tell you this: You WILL outgrow either of these machines quickly so if you plan on making this your main hobby then you will soon find yourself quite limited.