I don't have 1 singular shirt to rule them all, no, but I do have various shirts that could be considered favorites for various reasons.

Our headmates have their own preferred style/aesthetics which we associate with them, for example, we associate Clover a lot with nature themes (hence the name Clover), and so earthy colors like brown and green tend to go well for faer. Like our default belt is our pansexual pride belt but that's a bit more colorful than what Clover likes to wear so we'll switch to this cloth belt we have that's brown and a muted red if fae's going to be fronting. Because of this aesthetic association with some headmates, we do have a few shirts that we consider as belonging to a specific headmate, and those can be thought of as favorites.

I'm actually wearing Clover's tshirt right now, which is a black tree on a brown background with the leaves colored like a rainbow.
We also have a shirt that we consider to be Daisy's shirt, which is our 2019 Zipcon tshirt, mostly because it looks a little silly and it's yellow (Daisy very much likes yellow).

Recently elke bought us a tshirt that says Akron in rainbow lettering so you can count that as another favorite.

We have a few button-ups we enjoy wearing, especially a yellow & blue flannel we have.

We have a hot pink as fuck cami we enjoy in the summer and maybe loosely associate with Cara.

We also enjoy our 2020 Zipcon tshirt.

And we have some few tshirts that are pink and purple, they aren't special but we don't have enough pink/purple in our "wardrobe."