I am considering having a frame made by a custom builder and agonized over tubing choices.
The choices are 631, 725, 853, 853 Pro Team.
853 Pro Team seems to be what most say is the "best" because it is lighter and thinner.
But the price is much higher. So I am thinking of going with 725 assuming they can use thinner tubes similar to 853 Pro Team.
725 is only slightly more expensive than 631.
725 UTS is: 1080-1280 MPa, 853 Pro Team UTS is: 1250-1400 MPa, so not a huge difference.
I am light so I do not need a very stiff frame.
It seems there is a consensus that a frame with thinner tubes rides better although nobody can explain why but has to do with flex.
However bike frames flex very little so I am not sure if this is valid.