No Skill is truely better than one another each one is good in its own rights you just have to decide what you want to do with your character. Let me outline each below:
Absorption (100 is cap and concentration can only get to 50)
Whenever you are hit Absorption, when toggled, has a chance to absorb damage and turn a percentage based on your skill into life. It does use spirit points though, and if you cannot get to 100 concentration you wont be able to regenerate spirit points without a visit to the reverend. So probably not the best for the barbarian but is a good complimentary skill.
Druidy (75 is cap only have 20 mana)
Druidry is good for healing because of the regen spell. using this spell compliments healing really well because it can make your life go up even faster. Mana does regenerate on its own without concentration so it might not be a bad skill choice, there are other spells as well in druidry as well that might be useful to you. You will eventually raise your mana with more knowledge/intelligence so I wouldnt be too concerned about it.
Prayer (75 is cap only have 20 mana)
Prayer is not great for healing since you can only get 75 of the skill because the healing spell prayer offers requires higher skill than that to cast , prayer does however have the consecrate weapon skill that is a great spell for doing extra damage to undead and evil players.
Healing (200 is cap)
You probably want to raise this as your primary, the higher you get it the faster you will heal and the greater amount you will heal. This is a must for a barbarian, the decision you have to make is what to compliment this skill with. Oviously drinking healing potions go nicely but even beyond that it may be nessecary to have an additional healing skill.
Rejuvenation (200 is cap)
This skill is probably better in pvm, but you never know it might go nicely with the hiding skill. This skill requires no resources unlike healing which uses healing salve but it requires you to be out of combat and standing still to use it. At high skill it should provide significantly faster gain over healing.