I'll wear a T over a woven shirt any day, so it's a staple in my wardrobe. How I wear a T depends on the type.
For me, an basic, solid-coloured, cotton T (long- and short-sleeved) usually gets worn on its own with jeans or shorts for casual wear. If I wear a topper, it's usually a lightweight casual jacket like a utility jacket or something along those lines. I usually have a stash of these tees in neutrals and brights. I've finally realized that spending a bit more at BR or J Crew to get a tailored fit and a nicer cotton knit works better for me, but I've also found good ones at less expensive price points like Joe Fresh. Since most of these cotton tees get replaced after a season, it's nice to find good-fitting ones at a reasonable price.
My better tees are made of a fine silk knit and I'll wear them for all kinds of occasions, dressing them up or down as the situation warrants. They are all fluid fits so they look good on their own since they drape and tuck nicely. Most are solid colours. They are my travel staple, and with a bit of care, last for several seasons. Eileen Fisher makes some nice ones.
I've lately fallen in love with J Crew linen tees for summer as a slightly nicer looking topper for summer pants and skirts. These are the only patterned tees that I own. Again, I'll wear these tees under all kinds of toppers because they are fluid fits and fit nicely under all my jackets and sweaters. The solid coloured linen tees are particularly nice for colour blocking in the summer. I'll wear a cobalt blue linen tee with my white jeans, or a blue/white ikat-patterned skirt, finishing it off with a pair of sandals, a nice watch, and my sunglasses--super cool but polished enough for me.
