New to SmartThings should I avoid Wifi devices over alternative Z Wave or Zigbee devices?

2019 Update:

Everything in my post above is still accurate except that we are now up to V3 of the smartthings hub (still with reliability issues, though), and staples discontinued the connective line.

Oh, and the Amazon echo has become a much bigger player for those just looking for something simple.

The following 2018 FAQ explains why someone might choose smartthings over some of the competition: