I have, but it was twenty years ago - almost exactly - I'm getting old....
Palenque is one of the most impressive ruin complexes you will ever see, but there are controversies about how it was restored. Agua Azul is a park built around a series of ridiculously beautiful turquoise pools. You can see both of these on day trips from Tuxtla. There are huge Bay Snook in Chiapas rivers, the world record was caught there. San Cristobal de las Casas is a colonial town in the mountains that is worth a stopover if you are traveling around by car/bus, but I don't know if I would make a trip there specifically.
Not that Chiapas isn't cool, but Oaxaca has a lot more to offer in a lot of ways.
Edit: Here I am telling you about Chiapas and you probably know a lot more than me.

Anyway, I've been to Chiapas once, but I really like Oaxaca, been there ten times or more. Mostly we go to Jalisco these days, because flights are cheap and my uncle owns an apartment just south of PV. I've even spent a few weeks in el DF.