I don't necessarily have a "favorite" but I have some that get used more than others for sure. My MM251 Miller MIG welder and Dynasty DX300 TIG are my two welders, my 14" vertical bandsaw gets used a lot as well as my Jet 7x12 horizontal bandsaw.
The one piece of equipment that gets used probably the most is my Wilton 6x48 belt/12" disc combination sander. It seems as though there is always a burr that needs to be removed or a corner that needs rounding. That disc sander/belt sander gets used a lot.
I don't know what I am doing wrong as many people said their 4 1/2" angle grinders are used so much and I hardly ever use mine.
Most of what is seen in these two pics are my "go to" fabrication tools.
And here are the other two pieces of equipment that seem to get used the most next to my welders and disc/belt sander. Lathe and mill.
All in all a pretty loaded question as all my tools and equipment serve a purpose and really no one is more valuable than another. The one I am using for the intended job is the most valuable one at the time.
Mike.