I'm just getting started and thought I'd share my experience for any of you that may be trying to decide what paper to get. I ordered the sample pack of Light Inkjet Papers from Coastal and so far I've had the opportunity to try out both JPSS and Red Grid(both come highly recommended in this forum). After printing out the designs, I laid them side by side and noticed immediately that the black on the Red Grid Paper is truer(darker) than on the JPSS. I also noticed a slight grid texture on the Red Grid whereas the JPSS is more even. The same was true after printing them onto some white 100% cotton Gildan T's. The JPSS does have a little softer hand. Although the difference is noticeable side by side, they both came out great and I don't think you'd be disappointed with either paper.
If you want a darker vibrant black, go Red grid.
For a softer hand, go JPSS.
Printed on: HP Officejet 6500A Plus using Normal quality setting and standard inks that came with the printer.
I hand trimmed the excess paper around the edges(I haven't dropped the $ on a vinyl cutter yet).
Heat Press: Hotronix STX20 - 16"x20"
For JPSS: 365 degrees for 30 sec. and a repress for 5 sec. using silicon sheet.
For Red Grid: 350 degrees for 20 sec. and a repress for 5 sec. using silicon sheet.