Both are excellent and the differences are small. XTOL is a little more of a pain to mix due to the minimum 5L packaging. Some people prefer replenished regimes. I prefer to use developers one-shot.

XTOL will tend to give slightly higher film speed than D-76. But it is difficult to generalize as it depends on the film. Acutance is virtually the same, but again this could vary depending on the film. XTOL seems to give slightly finer grain, but my tests were all with tabular films so I don't have data for Tri-X specifically.
I use both developers with FP4 and Tri-X in small and medium format. I agree with the quote above with a few exceptions. The pain mixing XTOL at room temp is the amount. Its easy to mix but I don't use over 3L in 8 months. It keeps 2x longer in a 1/2 filled container vs D-76 (2 months shelf life). XTOLs 1/3 speed increase is real. I have original XTOL development charts for 1:2 and 1:3. 1:3 produces very sharp images with highlight compensation. XTOL gives a touch more micro contrast. But, negatives are only a tad better than D-76 and you may not notice in a 5x7 print.

One last pitch for XTOL. It is more Eco friendly unless your pouring unused chemicals down a drain. The answer is to share with a friend.