I got fed up with undershirts which shrink funny, or are too short and come un-tucked easily. So, I decided to try a bunch, and figure out which was best.
Without question, this is the best undershirt I now own. The next runner up is as far away as Kia is from BMW (personal opinion).

What makes this a great undershirt:
Length: It's long enough without being "big and tall" to stay tucked in.
Feel: The cotton is very supple, stretches easily to conform to people with a larger chest size than mine. The thickness is good. It's not super thin. It is a little thicker, but doesn't feel hot.
Construction: After a wash/dry cycle to torture test the shirts, this one shrunk up minimally and evenly without losing shape or developing odd puckers in the stitching. The short sleeve is stitched at a an angle, more consistent with how your arm naturally hangs. Other shirts are more of a T shape, the arm-pit of these is a much smaller angle V.

If I had one complaint, it's that the color is not pure white. It's subtly off-white in the same way your house trim isn't pure white, more egg-shell. It's noticeable when next to other pure white T-shirts or button downs. One of the other brands I tried was so white it was almost blue, but that could be optical enhancers.

Unfortunately, this comes at a price. At mid $20's for one shirt, it's easily 2-3x the price of other shirts. If the price doesn't bother you, this is a stellar undershirt.