"Walkaround" prime for FF?

[Hillsilly]

Carrying big lenses, a tripod and a backpack full of gear is good exercise.  That's why we're all fitter, stronger. healthier, better looking and more interesting than non-photographers.   

[tonyp]

I'd recommend the 35L 1.4   AMAZING LENS and tack sharp from f/2 on up

[dolina]

35 and 50 were the street lenses of Bresson. Choose the f-number of your budget.

[EOBeav]

I recommend the Canon 50mm f1.2L.

If you've got the bucks, sure. But for my money, the difference in IQ is negligible.

[ecka]

If there was a single best prime for everybody, then you wouldn't ask for advice, because the answer would be obvious. For me it is 35 or 50, but many are using 24, 85, 135 or even 200. Choose what is better for your style of photography.
Maybe it's just me ... but if you want to buy something and you don't know what exactly you want to buy, then perhaps you don't need it.

[Michael_pfh]

If I only had 1 prime lens, it would be the 24mm.

Why would you pick the 24mm?

It is wide enough to take pictures of landmarks and people.  It is a compromise, I obviously picked the 16-35mm and still am ok with it over the 24 (TS or f/1.4), but I think the 24mm would still work the best for a one prime camera. 

If I were going to a national park, I would go with the 17mm or 14mm...

For me the 24 is too wide to be my walk around (on APS-H), die 16-35 does a much better job so if not the 50 1.2L the 35 1.4L could be a good choice...