Should I buy a CNC laser or CNC router?

This would all depend on what you are likely to be cutting or engraving. A CNC router would be used for sheet work MDF, Ply, composites, hardwood, metals, soft stone etc.. With a router you can change tools for a specific material and finish. However, if you are cutting acrylic you will not get a crisp finish. The laser is good for thin wood based material but will leave a black edge around the outside as the laser burns through or on material. Acrylic on the laser will have a polished edge if set correctly. The laser can etch into glass, wood, slate, granite, perspex and some metals. In an ideal world both together would be a match made in heaven as you could cut your desired shape and etch into it afterwards.