A month or two ago, I bought a striped kuhli loach from a pet shop since it was the last one and I felt bad for it. After getting it home and doing more research, I saw that they prefer to live in groups. So, I scoured every petshop (including Petsmart, Petco, Pet Supplies Plus, all the locals) for more striped kuhlies, but to no avail. So, I settled and got the black kuhlies instead, though it's my understanding that they are actually a different species from the striped variety.
Anyway, my experience thus far has been that the striped kuhli comes out at pretty much any time of the day, usually for no more than 20 - 30 minutes at a time. Then he'll disappear for a bit, and come back out again. He isn't very shy at all.
The black kuhlies on the other hand, I've only seen a handful of times since putting them in the tank, and now I'm curious if they're even still in there. They'd strictly only come out after dark. And when I'd get up in the morning, before the lights came on, they'd hide the instant they heard any noise or saw even the faintest light from the lamp in the other room.
So, anecdotally, I'd have to say the black kuhlies are far more shy than the striped variety, though, I imagine in different tanks, with different conditions, and different occupants, the experience might not be the same.