Gem and the stats of it

[Qelacien]

Hey guys, im playing sin and i think Citrine gem is amazing for us...

on that gem you have 2 different options,

1) Drain

2) Additional Damage

is that Additional Damage really that matter? i mean 120 Additional is kinda nothin, would you take the Drain Gem for sin?

 

and Peridot gem, what do you think about it.

what does this Immune gives? 

would you use it instead?