I have a Go! What I like about it is that it is compact, lightweight, portable, and easy to store. The dies I like are the irregular shapes -- triangles, tumbler (both sizes are nice!), hexagons, circles, chisel. For myself, I prefer cutting strips with the June Tailor Shape Cut mat. I also find it easy to cut squares with a ruler, so don't use the Go! for that.
The Go! Baby is awfully limiting, in my opinion. I would watch for a sale on the Go! Maybe Black Friday?