What type of surface are you working on (I presume your garage floor)? Coincidentally my wife and I just got done doing this in our basement this weekend. We actually ended up doing both. We pulled up the old linoleum tile floor and wanted to stain the concrete, so we used a product to loosen the glue, then scraped off most of the large chunks by hand. After that we used one of the rectangular floor sanders with a heavy grit paper followed pad to get off the rest of the glue remnants and odd texture off and then smooth out the sanding scratches. Our last step was to etch it to make sure we had a consistent texture for the stain and the product we used was an etcher/cleaner to make sure we'd get consistent penetration: no remaining sealer or other chemicals left on the surface. Part of what we wanted to stain was our laundry so it had god knows what bleach/detergent spilled on the floor so we wanted to make sure we got as much of it off as possible. Turned out pretty well for not having done it before. Floor sander was $45 at HD for 4 hours. Not bad.