I think it depends how much damage you are trying to heal. If they are just a bit raw and painful, I'd say hydrogel because it's cool and soothing. If you are trying to heal badly cracked or scabbed nipples, I'd use breast shells. Just speaking from my personal experience. I had bad damage, cracks and scabs, and I found the breast shells helpful because I could put on nipple cream, Neosporine, etc and it would stay on and not just wipe off on my breast pad. It also really helps to rub a bit of expressed milk after each feeding/pumping and let it dry. Good luck!
After feeding try to air dry your nipples, it's also helpful to squeeze a little extra milk out and allow that to sit on your nipple and dry. Once they are dry then apply lanolin cream so you aren't chafing once you put clothes on.
Lanolin is amazing! I used the breast milk on my nipples and applied the lanolin on over that. Lanolin heals without forming a scab so it may not appear to be working but it is.
Re: Healing raw nipples… I'm confused.