Been at this game for I think two weeks, awakened my Light Elven Ranger for the heck of it, well aware that he's a glass cannon what will eventually get replaced by my shiny Water Pirate Captain (than you anniversary coins for those 150 summoning stones). And today I wound up with more Elven Rangers because the RNG thinks its funny sometimes. Are any of them must-haves or do I just use them for skilling up Lucien while he's still fun and viable?
In short: Fire, Water, Dark elven rangers are the ones to keep. Fire Elven Ranger is a great mon, and works well for Necro as I understand it. Water one not as highly sought after but can work well on stun teams. Dark one is cool too but hard to get. Wind is meh and food for others. I fed my light one.
Don't feed light one. Keep it. It's a Light monster, and you might never get another one.
Fire is the best Elven Ranger, who is probably the best supporter for NB10. Dark works well in NB10 as well as a DD unit. Wind can work in NB10 as well. Light and Water aren't very impressive. But still keep the light one due to the reason I mentioned above.