Blind Fighting by far. It totally changes your PC.
I will say, usually when I DM and in one of the games I play there is a houserule that every PC regardless of class gets Two Weapon Fighting at 1st level (I stole the idea from the other DM).
For some reason it is impossible to get players to follow the rules on light weapons and just giving them all Two Weapon Fighting fixes it (well it doesn't fix nick, but it fixes the errors in damage and the slowed gameplay). Without this you are in a combat and a player hits with his dagger using nick or using a bonus action and does 4 damage, then next turn he does 3, then 4 turns later he does 7 and I'm like 'wait how can you do 7 with a normal dagger using a light attack' ..... 'oh I forgot and I was adding my strength' ....'did you add it those other rounds too?'......'yes' Or they are using D&D beyond or a VTT and they can't figure out how to roll the light attack instead of the regular attack.
Easier just to let everyone add their strength/dex all the time with the bonus attack. It buffs Rogues a bit and lets Paladins, Fighters and Rangers that fight with 2 weapons choose another style but other than that it has little effect on play other than players not screwing it up consistently and having to correct them.