General

In my personal biased opinion, Nightlord is the best choice, after playing all 3 of these classes past 200, I'd have to say that it is somewhat dependent on what you plan to do for a majority of the time.
If it's just training then it's probably irrelevant but for Xenon, beam dance is quite good on linear maps for grinding as is their mobility. They also have a few mobbing skills and Snipe is really good for bossing.
Phantom of course has the most diversity out the choices above as I'm sure you are aware, can use a vast array of skills. Arrow Platter is a nice bossing skill since you can set 2 at once as well as you have a wide range of buffs at your disposal.
However i find that NL would have the be the most fun of the 3. Mobility is very good as is the DPS since they are fast attackers (If I remember correctly, after using MPE Green Potions they don't require the use of 'decent speed infusion' as speed will be capped out).

Realistically, it will come down to preference though. I personally like the feel of Nightlord as opposed to Phantom and Xenon, However this might not be necessarily the same for you. A little bit of trial and error might go a long way to figuring out which you enjoy the most. You can play for damage but what's the point if you don't enjoy it.

Good Luck.

Is no one questioning what good fortune has gotten him 80~100b? Anyway, as said, phantom is the strongest with that amount of funds. Although you could technically fund a phantom and nl and possibly a xenon too with godly thief equips. All you'd have to do is psok them and get a weapon/secondary for all of them.

if ur going for damage, Phantom>NL>Xenon as stated several times already. Don't worry about the nx or whatever u spent on ur Xenon, its nothing in the long run.

NL is the way to go

So, just so I'm clear, I should make a phantom?

pure dps wise:
Phantom > Nl > Xenon
Honestly don't see why people hype xenons damage so much, when it comes to end-game bosses they fall behind a lot of the classes, the only good thing about them atm is that they're generally easier to get range on and farming is super easy since beam dance doesn't have a timer.

Phantoms do a lot of damage, and are also quite fun.

Do night lords even come into comparison? lmao ._. i feel dumb for using royals and perm nx on my xenon now...

And the people above me have no idea what they're talking about. Make a Phantom if you care about damage. If you had only 20 B I would have said to go for a Xenon, but at the 80 B mark, Phantoms completely outclass Xenons in terms of dps. NLs are both more expensive than Xenons and weaker than Phantoms, if you want specifics you would have to ask someone else though.

Phantom is infinitely going to be fun because you'll have every explorer's attacking skills. I'd recommend funding the phantom.
EDIT: Forgot you wanted highest damage output oops
make a xenon for damage but phantom for fun

Damage wise probably Xenon, but I personally think Phantom and Night Lord are more fun then Xenons. Holding Beam Dance and walking around doesn't seem so fun to me. Phantom and Night Lord offer more diversity.