The truth of the matter is that you usually don't have many options when it comes to which Realtor lockbox to use. The local Realtor Association typically chooses one type of lockbox, which essentially has a monopoly over that local area (e.g. Phoenix, Las Vegas, Detroit, etc.) Once this monopoly is in place, you either use the Realtor lockbox they chose, or you don't use a Realtor lockbox at all. While you could lobby the Association to choose one particular type of Realtor lockbox when the contract comes up; the decision would ultimately be theirs, not yours. Using any lockbox besides the chosen lockbox system would be pointless because other real estate agents would not carry access keys or keycards to access your listing.
There are currently two providers of Realtor lockboxes: Supra and Sentrilock. Supra is made by GE Security, Sentrilock is an independent company; however, Sentrilock did receive venture capital funding by the National Association of Realtors (NAR). NAR was afraid that without a strong competitor to Supra, Supra might exploit its position in the marketplace by raising prices, providing inadequate service, etc. When a local Association of Realtors decides on a lockbox contract, they invite both companies to bid. The companies try to showcase their pricing (per lockbox and user fees), technology (e.g. access logs, live key updates, real-time information), equipment (e.g. illuminated keypads), compatibility with smart phones like iPhone and Android, and customer service.
Besides just not using a Realtor lockbox at all, the other option is using a mechanical contractors lockbox that you find at any hardware store. While they do not have many features you would find in a Realtor lockbox, they do allow a basic way to grant access to your property to others. They are also cheap: typically costing around $30 while some Realtor lockboxes cost over $100 with many added costs (usage, insurance, training, etc.). Some associations, perhaps prodded by their lockbox companies, have taken steps to eliminate this option as well. The first rule they can put in is making sellers only be able to opt out of using a Realtor lockbox by putting it in writing. The next rule can be requiring anyone using a mechanical box to have a Realtor box on the property as well. The final rule would be to just ban mechanical lockboxes altogether. By either fining the Realtor or removing the MLS listing, the rule has real teeth.