Best brands for plain t-shirts?

I've been wearing Gildan for quite a few years. Great quality and reasonable price.

I'd say Hanes or Fruit of the Loom, either would be a good choice.

http://www.uniqlo.com/us/women/tops/t-shirts.html

or

https://www.everlane.com/collections/womens-tees

Dirt cheap but adequate quality and good cotton. Especially the Supima cotton t-shirts.

But if just want t-shirts for wearing around the house then a pack of Kirkland T-shirts from Costco will serve you real well.

Beefy Tees.  They're nice & thick & made with exceptional quality!!!