there is no difference. const binds to the type to its left…unless it is the first part of the declaration in which case it binds to the right.
See: https://isocpp.org/wiki/faq/const-correctness#const-ref-alt
Personally, I find that const T &x reads better. According to this, Bjarne also prefers to put the const first. Specifically because the keyword was originally going to be called readonly and readonly int x reads better :-P.