Favorite... as in most-used, or best-liked, or what? And can I factor-in time and place?
On the road, my most-used is
K20D + DA18-250.
Indoors (low light), the
FA50/1.4 or (new to me)
Sears-Tomioka 55/1.4, but a new 24-28 f/2 might win.
Indoors (high light) on digital,
K20D + Zenitar 16/2.8.
Indoors (high light) or outdoors (small space) on film,
ZX-M + Lentar-Tokina 21/3.8.
Outdoors (small space) on digital,
K20D + Nikkor 85/2 (modded).
Outdoors (open space) on film,
Argus-Chinon CR-3E + Vivitar Ser.1 Ver.1 70-200/3.5.
Those are my most-used. The 21/3.8 is just about married to the ZX-M. The Vivitar zoom is just about married to the CR-3E. (Sorry, that M42 Argus-Chinon beats out the Spotty II.)
But my FAVORITE, the combo that's most INTERESTING to use is:
K20D + Schneider Betavaron 3,5...11/0.08 fixed-focus enlarger 50-125/4-5.6 zoom on 30mm tubes. A 25-50mm helicoid would make use a bit easier and I wouldn't have to add more tubes for macro work.
That brutally sharp and heavy (800g+) Betavaron is a wonder. I focus by moving and zooming. Every move changes the framing, so shooting an image requires a slow fore-and-back dance. That's why I want a helicoid. The lens setting are marked for production darkroom work, not for photography. Zoom levels (presumably an enlargement scale) are
3.5, 4, 5, 6, 7, 8, 9, 10, 11. Aperture marks (presumably brightness levels) are
1, 2, 3, 4, 5. Not an f-stop to be seen. I'd have to do photometry tests to calibrate the aperture, but why bother?
Forget all about f-stops and focal lengths in general or macro shooting. The only important number, in Av mode, is the shutter speed; for all else, just wing it. The five iris blades close to a star-like opening but bokeh is creamy. I've found nothing else like it in ~55 years of shooting. Oh yeah, I got it on the bay for US$70, marked down from US$3500. Such a deal!