I've had a ton of threadless shirts for close to 2 years. I've had to retire some along the way for stains and such, but they last pretty well imo. They do shrink after a while due to a lot of washes, but I don't mind as I like a tighter fit.
As for comfort, I have no problems with them. They feel perfectly fine to me.
Edit: If your familiar with American Apparel shirts, then your in luck. A majority of thread less shirts are printed on them.
I've owned around 20 or so of their shirts through the years and the quality isn't as good as it used to be. Not horrible, just that they feel thinner and fit differently than before.