That is a hard question to answer as it requires knowing what your goal is, as well as your play style. If high physical damage is your thing, Nia (kitty) as a warror is good for raw damage, as is Celeste (elf) as a ranger. This combo will give you a party that can smash through the early game with high damage and flawless single turn victories, such as imp-succubus and goblin. Even with a full team if you let Nia get jacked by the spell then the other will usually die with one shot from the arrows. The only issue with this team is that you are forced to rely and potions which, although will help, are not as good as either of the magical heals. Another thing about this team is that while Nia will really only have to worry about spell damage, Celeste is still as brittle as ever and should be treated as a glass canon.
Nia (warrior) is the heavy melee hitter of your group and the tank. Her warrior currently gets the best weapons very easily and early if you do quests, and has heavier armor. Celeste (duelist) is supposed to be a weaker, but quicker and more accurate version of this, but I have seen her miss far more often than Nia, and does far less damage while being harder to get upgraded weapons as you need to progress and craft. While she is faster, as in she gets to attack faster than Nia would, the lack of damage and durability makes her more of a consolation so shaman Nia doesn't get jacked before she sets her stuff up. Duelist also doesn't have a usable skill, aside from the generic hentai test, so until this is updated, she is an attack spammer. Unless you are using Nia for something other than melee, this is probably her weakest role as she is supposed to be a quick and accurate character. However, having not played her assassin class, I can not confirm which is weaker.
Comparing the two magic heroes, I would have to give it to Nia (shaman) since hers are all group based and continue for a few turns. Both poison and nature heal take effect the turn they are used, so you damage the enemy team or heal yours, then do their thing after the turn for either you or the enemy. Compared to Celeste (priest) who, while doing more per single use, has to be able to use the spell or it's useless. Considering that preparing for a charm or futa by casting it the first turn will let you stay on top of whatever damage being done, assuming you have the defense to survive their physical attacks, you can either attack while the enemy is busy or heal to keep a less durable character alive. The same applies to her damaging spell which causes damage, then after every enemy turn causes damage. Since it seems to do the same percentage of health loss to all enemies regardless, it is deadly at every encounter and smashes bosses. Being able to kill units while you keep someone alive is invaluable. Poor Celeste just becomes a target since her high damaging spell triggers aggro and the enemies seem to target high single use attacks over a higher attack that is a composition of all units. Since her heal can't work if she is stunned, it loses to Nia's.
The two quick classes are supposed to be nice at smashing heavy armored units, but as I have not seen anyone that would constitute as heavy armored, they would mainly be for their speed. Both classes also seem to hit about the same as the heavier hitting classes, just with less damage Honestly, I have only used Nia's (monk) version so far, and the only difference was that she did much less damage, but could attack faster. This can help if you were to smash through a weaker front line troop so that another front line troop could use a stronger attack on a back line troop, but so far that isn't as relevant as by the time you can do that, the enemies in the back would be pretty weak anyway. Still, one less charm could save some time, or a potion at least. I haven't tried Celeste's (assassin) version of the quick class yet, but I assume it is the same as the others, which is her being faster with more accuracy, but weaker both in damage and defense/hp. Again, unless you need someone to tank for Nia, or just another person to do damage without magic, I don't know if I could recommend her for a melee clas.
As for archers, I have only tried Celeste, and this seems to be where she shines. I tried this with Nia's warrior, my first time for this as well, and she was able to one shot just about every imp-succubus and even some of the big ones. She is still as brittle as ever, but now she is a true glass can and actually works well with any other front line unit. I mentioned her and Nia's warrior in the first part, but it works with the others as well, and could even work with the monk class as long as you keep the damage off her long enough to kill the back line units. Although I haven't tried it, this could even be a possible team up for the shaman (kitty mage) as the healing could keep kitty alive while you snipe people. Although, I would wait until more updates to to see if such a team is strengthened. This would be my preferred class for Celeste as she can stay back and smash magic users before they can get a spell off, or even halve a bosses life in a single shot, although if you are new you may want to have her mainly as the healer while Nia tanks, at least until you learn the units and how to manipulate the enemies better.
Now, for the part that is probably what you will want once you have shot and hit enough creepers, the lewds. Losing causes some sexy goof, but it only works for the last party member tapping out to whoever finished them. This is quite annoying in some cases as front lines can only hit front like, so the second dungeon is perhaps the hardest to get who you want without specific formations. For this, you could try using Celeste as an archer and Nia as a shamen. You may be brittle, but you will both be attacked by whomever you wish. Another reason is that both girls can hit whomever they wish, although Nia will end up killing anyone if you spell does too much damage, so you may just wish to use her for the group heal. Of course you could use any combo as long as they are both in the front or back, the idea is that Celeste can butcher who is likely to kill the wronger party member first, or take the last hit, while Nia casts heal, then tanks as well as she can. I haven't tried Nia's archer, but that may also work well with Celeste's high damaging single hit spell, which is really the one time you want hers over Nia's team-wiper. Just remember to keep Celeste from attacking until a stun spell has hit the tank of your party if you are using her as the archer.
This is what I have learned from playing the current free version, so things may have changed for those playing a current build. My advice is make a team for what you want during your current playthrough. If you want sexytime, try what I mentioned, if you want to kill people quickly with single shots and little mana usage, warrior kitty and elf archer, if you want something with magical healing, try shaman, for balanced you could do priest and warrior as that is more straight-forward. Finally, unless they change up the starting skills or add learnable ones, I would advise against certain classes in general, melee Celeste unless you just need fodder, and champion for others, Celeste with a bow every day. Until then, hope you get a use out of my little "character guide".
