Now to the goods. The best shirts for sublimation are still shirts high in polyester. Bella Canva, and Gildan Softstyle tees in the heather colors, offer some great options that are 65% in polyester. You can still use tees with 48%+ polyester, but the results will have a vintage look. I would not recommend using anything less that 48% polyester.
Here at DWD Tees we offer our DWD branded tees and they have a 65% polyester count. These are specifically great for sublimation, but can also be used for screen print transfers, vinyl, and screen printing.