What is the most popular wood finish ?

I would think cherry or walnut would be safe choices. A lot of the exotics can be too taste specific. Just use a natural stain and a clear coat. Make sure you see samples by whoever is doing the work for you.

Natural Cherry.

have REV 5's in bocote wood that Fritz had lying around

I think those particular speakers look best in maple or birds eye maple.

It depends on the brand and size. I think dark colours, ebony and walnut, are better on smaller monitors, a bit overpowering on large standmounts. I like cherry a lot, but if it's reall wood, not a veneer, it tends to redden with age. I like the real oak cabinets with a walnut fascia, on my speakers. My wife got to choose that.

It really depends on the maker. Different companies have different looking finishes, too.