Note that what i will say is after you have already done a playtrough of the game and also if you have transfered the good skills on each of the three characters, if you're playing for the first time it will be hard to just focus on some girls.
So if you really want a team that will just steam roll the game even on expert mode, your answer is Angel (will become dark angel later, that's what you want and you need lewdness lv 3 for that) + Dark fairy + Kraken. You can only buy those three girls on auction and Angel especially have a high price.
Angel (Dark Angel) is your money maker with her skills making her gain absurd amount of money, even more if you transfer the good skills on her
Dark Fairy will enable you to basically do a free round of training (Up to 5 trainings if you have maxed her affection) with her skill. For her, slap her with the fortune skill of the oni so that you trigger the two skills when she have penetration training. Fortune Skill is for making a wealthy guy appear and if you make a Angel service him, welp here comes the money xD
Lastly Kraken. She's really useful because of her skill that resets everyone cooldown, making you able to use anyone you want directly.
Well if you really want a example, you should be able to find my save with this team and the skills i've put on them. The save is at page 23.