From a climbing standpoint? Either the Black Diamond Hoodwire (now discontinued, and I'll guard my stock with my life) or any member of the Black Diamond Rocklock family tree.
From a general usage standpoint, Trango used to make a wiregate called the Classic Wiregate. It wasn't as easy to clip as the Hoodwire, but it was more symmetric, so you could use it for carabiner brakes and things of that nature. It was my go-to utility carabiner, but since it wasn't as flashy as crabs meant specifically for the rope end of a quickdraw, it never sold well enough and so they took it off the market. Turns out that a purely functional, no-frills carabiner couldn't compete with objectively worse carabiners (the Black Diamond Light D, or ugh the Omega Pacific Doval) because it didn't look as "classic".
Many manufacturers make terrifyingly small full-strength carabiners, but my experience with them is that they are so small that they're difficult to operate, so I have a surprising number of effectively keychain carabiners that are actually rated for climbing usage.
Sidebar, for life-saving equipment, climbers are bizarrely obsessed with how cool things look. The parenthetically mentioned Doval was a terrible carabiner, but it looked kind of neat, like a classic car with modern influences. It had an ovalized exterior, but a D-shaped interior, so it had all the clippability problems of an oval carabiner (can you determine where the gate's axle is, purely by feel, in under a second? not on a smooth oval carabiner), while maintaining the D's principle weakness (and why oval carabiners remain popular): under bodyweight and higher loads, a nearly-correctly positioned d-shaped carabiners will shift into the correct position, leading to a nerve-wracking drop. Oval carabiners will not do this under bodyweight loads (but also might not when faced with higher loads, somewhat compromising their ultimate strength, which is, because of the design, also somewhat lower than a d-shaped crab). When hanging on really tenuous anchors, that little drop has caused said anchors to fail, so direct-aid climbers have favored oval carabiners, even though they tend to be objectively worse carabiners in every other respect.
From a general usage standpoint, Trango used to make a wiregate called the Classic Wiregate. It wasn't as easy to clip as the Hoodwire, but it was more symmetric, so you could use it for carabiner brakes and things of that nature. It was my go-to utility carabiner, but since it wasn't as flashy as crabs meant specifically for the rope end of a quickdraw, it never sold well enough and so they took it off the market. Turns out that a purely functional, no-frills carabiner couldn't compete with objectively worse carabiners (the Black Diamond Light D, or ugh the Omega Pacific Doval) because it didn't look as "classic".
Many manufacturers make terrifyingly small full-strength carabiners, but my experience with them is that they are so small that they're difficult to operate, so I have a surprising number of effectively keychain carabiners that are actually rated for climbing usage.
Sidebar, for life-saving equipment, climbers are bizarrely obsessed with how cool things look. The parenthetically mentioned Doval was a terrible carabiner, but it looked kind of neat, like a classic car with modern influences. It had an ovalized exterior, but a D-shaped interior, so it had all the clippability problems of an oval carabiner (can you determine where the gate's axle is, purely by feel, in under a second? not on a smooth oval carabiner), while maintaining the D's principle weakness (and why oval carabiners remain popular): under bodyweight and higher loads, a nearly-correctly positioned d-shaped carabiners will shift into the correct position, leading to a nerve-wracking drop. Oval carabiners will not do this under bodyweight loads (but also might not when faced with higher loads, somewhat compromising their ultimate strength, which is, because of the design, also somewhat lower than a d-shaped crab). When hanging on really tenuous anchors, that little drop has caused said anchors to fail, so direct-aid climbers have favored oval carabiners, even though they tend to be objectively worse carabiners in every other respect.