Basically, the quality depends on the raw material, and for a t-shirt, the yarn is a crucial element. The yarn made of long-staple cotton such as Supima, Egyptian cotton, or DCH or S-6 can produce an excellent Tshirt.
Then knitting with the appropriate gauge and soft processing treatments can enhance the quality of a t-shirt. Finishing with the right amount of hydrophilic softeners can add super soft handfeel.
The designing part is also essential, but there is no match to a regular basic round neck t-shirt, aka crew neck.
So a t-shirt made of long-staple cotton is the best.
A melange t-shirt is also soft and comfortable.
A polyester t-shirt with functional finishing. Such as moisture-wicking and quick dry.
The fabric should be blended with Spandex.