SUPRA is more normal in contrast. ULTRA is too high in contrast for normal use but meant for special purposes (eg. if you have low-contrast under- or overexposed negs, or like high contrast). I haven't used ULTRA personally, though, but I find that even the SUPRA has sometimes too much contrast, never too little. PORTRA was even milder in contrast but discontinued years ago.
SUPRA will probably be discontinued, so buy it while you can to freezer. You can read this in the datasheet and due to fact that it's disappeared in KODAK Website.
I've used AG Photographic. Excellent prices in RA-4 papers.