I had a goat with an 18.5 running on 3 cell before the 3 cell goat was out. I wasn't all that impressed with that system personally. I switched out to a Tekin RS ESC and a Tekin hand wound 35t and was a lot happier with the performance. I was going to switch out to a 17.5 motor but wound up going MOA in my Losi instead.
I had a brushless set up in my Axial when I had that and wasn't all that impressed with it either. Not enough slow speed response. It seemed to jump when you wanted it to crawl.
In a Losi Comp Crawler, go either way. In anything else, I would save your money and just go brushed. They're cheaper that way anyway.