General

Definitely NL because potions glitch at gollux so we cant heal for 2 minutes straight sometimes >.< DB's have higher avoid and drain, and shads have high defence

NL's in general need it the most because they have zero Evasion Rate (this is different from Dodge Rate), and Damage Reduction.
DB's have 70% Evasion Rate, and 20% Damage Reduction with Mirrored Target active.
Shad's have 20% Evasion Rate, and 60% Damage Reduction.

It also depends on the boss. Vampire would be best suited for a Shad at Gollux because they have close range attacks. DB's can move with Bloody Storm, and NL's can stay ranged, or move in the opposite direction of where he's facing on Hell Mode to avoid his breath at the Jaw. At bosses without % HP attacks, Shad's can tank the damage, and DB's can evade it altogether, leaving NL's to rely on their natural Avoid and 45% Dodge Rate.

I would say Night Lord as well since we are naturally squishy.

i would say NL since they're more squishy

omg mixed opinions... and since i already have a high level db, this is between shad and nl so which one? more suggestions pls

Shad or DB. It helps at times during gollux.

NlL's need it the most because they have the worst defense, have to spam 100's of pots just to train

Probably Dual Blades, since their Life Drain skill isn't too great nor does it activate often, and it allows them to solo PB statues.