I'm just looking into printing transfers for my own use. Here's some info I found:
Hot-Split: Easy to apply and leave a soft hand feel to the imprint on the shirt. There is no "rubbery" feel or look to Hot-Split transfers--they look just like the image was directly screen printed on the shirt. The only drawback to Hot Split Transfers is that they have a low opacity, and must be used on white, ash gray, or very light pastel colors. If you need a high opacity print on your shirts (e.g.: a white print on a black shirt), you will need to use Cold Peel Transfers.
Cold Peel: Totally opaque print, can be used on any color of garment and all colors of ink are available including metallics, shimmers, etc. . The drawback to Cold Peel Transfers is that have a heavier "rubbery" feel, as all of the ink is deposited onto the garment. Also, the transfer can't be peeled until it is totally cold, which means they take a little longer to print than Hot Split Transfers.