Best - I don't have a Garage (shed) yet, so it would have to be the slab I recently had layed underneath the house that is the foundation of my garage. Nothing worse that working on the dirt. other than that it would have to be my Triton 2000 work centre and my Hitachi 12LCH digital drop saw.
Worst - knowing that I have to put four walls, windows and doors up over the new slab.