XM is a proper mud tyre. I think the XG is the classic cyclocross intermediate chevron tread. The XL is a really good tyre too, but better saved for mud.
The XL is the proper mud tyre isn't it? XM is claimed for mud, but the tread isn't that aggressive and it seems to cope with intermediate conditions well.
I think I only ever used the XM in thick mud and didn't really rate them in that, so perhaps they are more of an all rounder. Good in a straight line but I had trouble getting around corners.
XM is a proper mud tyre. I think the XG is the classic cyclocross intermediate chevron tread. The XL is a really good tyre too, but better saved for mud.