SmartThings supports a LOT more devices than A+ a lot of which are through community written device handlers. However only officially supported devices will run locally. Once I realized that most actions are ( currently ) run through the cloud, I was turned off, given past experience with cloud based systems ( Wink) and the 5-10 second delay on triggers. However 8 months in that has not been the case, trigger response has been withing 1-2 seconds, so while not the 300-500 ms I was getting with A+, they are still tolerable.
To give you an idea of how many devices are supported, 8 months ago I had I think 37 ( maybe it was 47 ?) HA devices on A+. I now have 117 ZW and ZigBee on SmartThings. That doesn't include all of the LAN devices,
One advantage of cloud infrastructure is a lot of cloud to cloud integration with things like Amazon Echo, Harmony remote controls, Nest, IFTT, etc. As far as the comments about ST being " pay to play" that is incorrect . There are plans " in an upcoming release" ( we all know what that means ) to support cloud recording of IP cameras directly through ST. Like most cloud IP camera recording there will be a fee to keep your videos stored on their cloud. THERE IS NO FEE FOR THE HA SIDE OF IT.