Belt drive
A rubber belt instead of a metal chain, which makes it substantially quieter. This is the right answer whenever there is a bedroom above or next to the garage, and in most attached garages generally. It costs more than chain drive and the belt is a wear part, but the noise difference is not subtle and it is the thing people notice every single day.
Chain drive
A metal chain, the traditional design, the least expensive and the most tolerant of a heavy door. It is noticeably louder, so it suits a detached garage, a workshop, or an attached garage with no living space adjoining it. In heat like this a chain drive is arguably the more forgiving choice mechanically, since there is no belt to soften.
Wall mount, also called jackshaft
Mounts on the wall beside the torsion bar instead of on the ceiling. It frees the entire ceiling for storage or a lift, it suits high or vaulted garage ceilings, and it is quiet. It costs the most and it needs a door with a torsion system in good condition, because it drives the bar directly. In a Las Vegas garage with overhead storage racks, which is extremely common, it often solves a problem the ceiling mounted units create.
Horsepower and door weight
Half horsepower handles a standard single or a light double door. Three quarter horsepower is the sensible default for a double door and the right call for an insulated one. One horsepower and above suits heavy, oversized, or solid wood doors. Buying more power than the door needs does not make the door last longer, but buying less means a motor working at its limit on every cycle in 115 degree heat.
Battery backup
Worth it here. A summer outage in Las Vegas is not an inconvenience if it leaves you unable to get a car out, and the manual release on a hot afternoon with an unbalanced door is not a pleasant job. Battery backup is standard on many current units and inexpensive as an option on the rest.
Smartphone control
The genuinely useful feature is not opening the door from your phone. It is being told the door has been left open, and being able to close it from wherever you are. On a house where the garage is the main entrance, that is the feature people end up using daily.
What to check before buying anything
A new opener does not fix a badly balanced door, and fitting one to a door the springs no longer support will simply destroy the new unit under warranty. Run the balance test first. If the door does not hold its position by hand, the springs need attention before the opener does.