Erwin Park all day long! I've ridden it many times and taken my sons there when they were younger. I hate to overuse the analogy but its WC'esck but IMHO more scenic and rolling.
I've never ridden Hartlee Field, in fact never hear of it. Ray Roberts sounds familiar but I think it goes by another name (for the trail). And if its the one I think it is, then its legitimately a bit technical. Its got a decent bit of embedded sharp rocks and some chunk.
Later,
CJB