I don't know about Jiffyshirts exactly, but Gildan brand shirts are great.
If you would like to use a supplier that I know for sure has top quality shirts try Alpha Shirt Co. (
www.alphashirt.com) They have great pricing (same as Jiffy for the gildan shirts) and have warehouses all over the country for fast shipping.
I hope this helps, Good Luck & Welcome to the Forums!!!