Vixel vs Felicia

Depends. Vixel has 100% sleep resist but I wouldn't recommend using him for quests that inflict sleep because he's off element. Felica has a better resist skill (poison resist) than Vixel but it's not 100%. However, I would prefer Felica because she has a skill that grants a shield to everyone and removes poison so she's not that bad. Vixel had a pretty bad second skill. However, he does have a decent healing skill which is slightly better compared to Felica but Felica is good because she's good for any dark type dungeon because of her Undead Res.

Generally, Vixel is better than Felicia but seeing your team composition you haven't got so much to pair with Vixel psynergy so...

With a light team full of poison resist (provably oriented to Onslaught battle) Felicia can perform better (with a little help of poison resist from any wyrmprint).

Btw, note that felicia's second skill have got an effect to remove poison... totally useless for your team. Pretty much like the energy levels from Vixel x'D.

To sum up, the better "healer" are Vixel (he got a better healing power) but he doesn't fit properly on your team. My suggestion is about trying to switch both depending on the resistance of the content you play (poison affliction = felicia / any other dark content = Vixel). Actually Felicia is the only healer oriented to poison resist content... and sucks with her 50% and her general kit T-T