Double Rope Belay Devices:
These devices are intended for use with double ropes (though they can be used just as well with single ropes). As they are intended for use on multipitch climbers they are made as light as possible.
These belay devices are listed from stickiest to slickest (approximately) so for thin ropes the ones that appear first will be best, whilst for fatter ropes and situations such as sport climbing where you may need to pay out a lot of rope quickly, those lower down the list will be better.
If you want a device that has some sort of auto-locking/guide feature look further down the page at the Magic Plates.
Magic Plate-type Belay Devices (for instructors):
The following devices are intended to be used as a "magic plate", that is by instructors bringing up two clients. The advantage that they have over standard plates in this respect is that, when used correctly, they will lock off if one of the clienst falls. Their disadvantage is that it can be difficult to unlock them if you don't know what you are doing (see Andy Kirkpatrick's Escaping from and Auto Locking Belay Plate to see how to get out of a potentially sticky situation).
Although these devices can be used as a standard belay plate, they are quite a bit dearer and heavier, and there is not much point unless you also instruct regularly.
The photo on the right shows the original New Alp Magic Plate from which the generic name for these devices derives but which is no longer available.
Sport Climbing Belay Devices:
The devices listed below are intended to be either automaticlly locking or semi-automaticlly locking devices for use when sport climbing using a single rope. As such climbs are nearly all single pitch, weight is not so much of an issue.