One immediate difference is that sr.ht has a publicly-hosted version; I'm having trouble finding that for Trac.
Trac is also not JS-free, so for those who prefer to not rely on arbitrary Turing-complete code running locally without explicit permission, sr.ht has an edge there.
That said, Trac feels a lot more polished (unsurprisingly, given that it has a significant headstart in terms of development resource and time).
Right, Trac has an extreme head start; it was, before Github, practically the de facto standard answer to this "software forge" problem. But it also continues to work just great, and has a pretty decent ecosystem.
Trac is also not JS-free, so for those who prefer to not rely on arbitrary Turing-complete code running locally without explicit permission, sr.ht has an edge there.
That said, Trac feels a lot more polished (unsurprisingly, given that it has a significant headstart in terms of development resource and time).