Belay device debates get religious. Here's the practical version.
ATC (tubular)
Black Diamond ATC. Petzl Reverso. Same category.
Lightweight (under 3 ounces). Simple. No moving parts. Works with skinny or fat ropes. Can belay two followers at once (for multi-pitch).
Downside: no assisted braking. If you let go of the brake hand, your climber can fall. You have to always, always keep your brake hand on the rope.
GriGri (assisted braking)
Petzl GriGri. Auto-assist when a sudden load hits it. Easier to hold a hanging climber. Makes resting at the belay less work.
Heavier. More expensive. Doesn't work well with very skinny ropes. Still requires brake-hand technique (the cam can stall if you don't feed correctly).
When I use each
Sport climbing: GriGri, every time. Falls are more common, and the assisted braking makes hangs easier.
Multi-pitch: ATC. Lighter, works for two followers, doesn't require precise feeding in hanging stances.
Toprope beginner days: usually ATC. The rope management is simpler for someone just learning.
What I carry
Both, always. ATC lives on my harness. GriGri stays in the top of my pack for single-pitch days.
Common mistakes
GriGri users: the old "push the brake hand back" trick kills the cam and lets the rope slip. New technique: keep brake hand on the rope, feed with thumb on the camming lever. Petzl has videos.
ATC users: don't let go of the brake hand. Ever. Not to scratch your nose. Not to tie a shoe. Not for a second.
The Click-Up
Another assisted brake device. Lighter than GriGri. Some pros like it more. I don't. Personal preference.
Which first?
ATC first. Learn to belay with your attention, not with a mechanical assist. Then add a GriGri once the fundamentals are set.
