+1 to both Russ and Setch.
A variable speed router will give you more long term flexibility for general woodworking, furniture making (e.g. raised panel doors), use in a router table, etc.
For guitar making, I think a single speed is fine. I tend to use the router for cleaning up pickup cavities, neck pockets, electronics cavities, etc after drilling out most of the waste first, and for cutting truss rod channels, rounding over edges, etc. For that work, the bits aren't large and I haven't had any problems with a single speed.
I know others use a router for more e.g. flattening the surface of body blanks, initial shaping of neck contours, etc. I'll defer to those who do that.