Keep nails clipped and filed smooth.

The nail cutters all leave very sharp edges.

Use a doggy nail file to resound every nail after clipping them.

A medium color with a prominent grain like an oak. Dark will show everything. A less prominent grain like a maple will show everything. Glossier will show everything. A dark shiny floor with not much grain like a jatoba will look like you have a 4th dog from all of the hair that will stand out on it. Not to mention the doggy and people footprints that show on dark and glossy.

We installed natural hickory a year ago & have 2 40 lb dogs. Unfortunately one now has a brain tumor & slides all around. All I can say is thankfully we have a light patterned floor. There are many scratches, especially in the kitchen, but overall you don't notice them, although I know where there are! The light color does not show hair, even though I sweep up a little ball everyday. Probably not what you want, but just telling my experience.

I can't say for sure what is best, but I can say that we have unstained semi-gloss red oak floors that have lived through three big dogs (one at a time, though) and as much as 20 years and still look fine. The current 80 pound doodle loves to run and make skidding corners around, through, and over everything. Scratches just don't show. Dirt and dust show relatively little.
But drifts of black fur (she is unfortunately a shedding doodle) are another story.

I think any stained floor, especially if the stain was significantly different from the natural color, would present problems eventually.

I posted pics of the floor under the pegged oak thread below. I know this isn't the look you want, but it is darn near dog proof!

Here is a link that might be useful: Pegged oak floors