Any t-shirt is fine for heat transfers. What eer t-shirt that you like the feel of. I personally like the heavy weight versions of: hanes, fruit of the loom, jerzees, and gildan. I personally wouldn't go out and buy the most expensive american apparel t-shirt to put a heat transfer on. That defeats the purpose of the retro feel of the shirt. You'll be fine with a heavyweight t-shirt of any of the brands I mentioned above. Get whatever you find the best deal on.
Gildan Ultra is a good choice all around for quality and value. Sounds like Jerzees are a little softer and feel better, but they're also more expensive. American Apparel is a good choice if you really want something made in the US.
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