Underworks. Although I don't have experience with Double T.
I made one that was okay, but only for a day or so of wearing - I wouldn't have used it for everyday.
And from Underworks the only one I can recommend is the Tri-Top. The longer one just isn't as strong and the length isn't necessary and tends to roll up on people. Also, you will get sweaty like crazy. The Tri-Top is bad enough and I roll it up on very hot days, since there's no point in having it go down as far as it does.
I might re-hem them eventually.
Also, you MUST use the FTM sizing or it will probably not work very well. You measure around the chest at widest, and right under it - where a bra band would be. Add and divide by 2. Now, you still might have to exchange, but much, much better than using just the big chest measure.
In my experience, T Kingdom is only good for those with already small chests. Same for Lez Love Boat. They're nice products, but I wouldn't recommend to someone who had a larger chest - anything more than a small "B" cup, I'd guess.
Here is what I home-made : LINK TO PICTURE
It's really important to have the elastic in a "K" or "X" pattern, not just "around and around". Around and around takes more pressure to do the same thing and greatly increases discomfort.
The K/X distributes the pressure better and also applies it more effectively.
. Yeah, I don't really take pictures of myself often. Totally my Halloween costume.