This page lists links to buy all of the smart trainers posted on Zwift's Supported Trainers page. I wrote it because the page on Zwift's website as of Feb 18th 2018 does not have this info. It also lists some of the YouTube and written reviews and makes a recommendation on which you should get (TL;DR: get the Wahoo Kickr Snap). Link to the spreadsheet.
Wheel-On or Direct Drive?
Wheel-On Pros: Lighter, compatible with most bikes
Cons: Make sure tire pressure is right, tire is clean, tire slippage, tire wear, 5-10% power accuracy
Direct Drive Pros: No slippage, no tire wear, 1-5% power accuracy, no cals or minimum cals, a little more road-like
Cons: Need to match the # of gears, need to take tire off
Verdict: Get a Wheel-On: You save $600.00 with a Wheel-On, its lighter and compatible with most bikes.
Of all the trainers, I suggest the Wahoo Kickr Snap. Its compatible with Zwift, is $600.00 and you can get it directly from Wahoo.