There are three that are officially certified to “work with SmartThings,” so from that standpoint they have the best integrations. 2Gig CT100, one Honeywell model, and one RCS.
However, a lot of people prefer the Ecobee because of its zone sensors. @yvesracine has done a ton of work developing a device handler for it, but it can still be a fragile interface if either ST or Ecobee change something in their cloud. Doesn’t affect the basic working of the thermostat, fortunately, but it’s something to be aware of.