I guess I will go with ST2220T because at the same price point ($300), I would rather have the touch option with it where as the U2412M doesn't have that feature.
Any other monitors to consider, ? Acer T231 or HP touch?
I purchased a st2220t recently and my only issue with it is lack of a vesa mount, but recently saw a mod someone did where they use the stand to clamp onto metal plate attached to a mount and seems to work well.
It is a good touch screen as long as not expecting more than 2 finger touch which is about normal for current touchscreens, it is also using a infrared sensor for touch which is nice because it does not limit you the way capacitive does.
While tablets, laptops and some all in ones will get 10 finger multitouch I doubt there will be many standalone monitors and probably not reasonably priced.
So long as glossy screen and screen size is not an issue for you it is a good monitor.