Also, for anyone interested in a more down to earth introduction to Lua, without the stardust and mystical references, I like this beginners guide.
Choice is good.
Again, though, remember that in the smartthings environment, you aren’t going to be writing complete programs. Just edge drivers, which are fractions that get embedded into the hub’s firmware. So you can play around with standard Lua as much as you want but when it comes to using it with smartthings you’ll be limited to the libraries and syntax that smartthings allows.
Here’s the official smartthings introduction:
Tutorial | Creating Drivers for Zigbee Devices with SmartThings Edge