My school didn't have a Tri-Delt chapter, so to answer your question, "What do you think of Tri-Delts?", my response is "I don't.".

Here is a question for you: "How do you feel about wearing 3 delta's on your sweatshirt?" IMHO, it doesn't look as "interesting" as say, wearing a combination of different letters on one's sweatshirt. Ditto for the Tri-Sigma's.