I think they are both great but both have some diferences.
1. Life Regeneration
Slowly, but Cooldown is short, so I'm thinking.
This skill is great, it was used by a lot of players before there were big updates, this skill is cheap to upgrade, simple to use, at max level this heals you for 15 seconds, cooldown is 25 seconds so you have to only wait 10 seconds to use it again so its quite powerful - the more hp you have the more effective it will heal you so will feel like a terminator.
2. Instant Life Regeneration
I feel like the amount of recovery is irregular.
This skill is also great, but i think this one is more expensive, also i think it heals about 70 % at max level but due to its cooldown and that its more expensive i think life regeneration is better.
And in my honest opinion, The skill that you need to invest beside these skills is damage boost, also csed 'db' by many players in short. Also this is an aura skills which almost all ppl are using in this game becsuse its the best i think.
Its quite expensive but with it you will kill much faster stronger animals, and if you need heal you can always use a totem regeneration heal skill which is great and with time if you upgrade it - you don't even have to upgrade area life regenration or instant life regeneration, becsuse that skill resides in totem tree skills so you can use damage boost + totem regeneration and i think thats way better