There’s no one “best“ because different people have different needs and preferences. There are quite a few locks which work well with smartthings, so it just depends on what you are looking for. It also depends what country you are in, as the device selection does vary considerably.
The most popular US locks have probably been the Z wave models of schlage and Yale. Both are good locks with somewhat different features. August is also popular for those who want a retrofit lock which doesn’t change the exterior hardware.
Kwikset is a budget brand which is about two classes lower in quality based on standard lock ratings. (It has a lot of plastic parts where the others have metal.) but it’s definitely cheaper, and is popular for that reason with those for whom budget is a top priority.
The following discussion thread is old, but pretty much still applies. ( The topic title is a clickable link)
All of the locks on the official compatibility list are OK. Danalock tends to get lower ratings than the others, but the newer models are considerably improved over the originals.
https://www.smartthings.com/products/-/filter/categories/door-locks
So again, just depends on your own preferences. Different brands come in somewhat different colors, the Yale is probably the quietest, August has a number of features that the others generally don’t, Schlage has more colors…you just have to do some research or else give us more information about what your own preferences would be. Choice is good. 