Depends, do you mean the ones that are on Steam or others too?

Also it depends of what you are interested in, in my case those are ones that I consider the best out there (those ones are in no particular order):

Summertime Saga

Love & Sex Second Base

Another Chance

Paradise Lust

A Town Uncovered

Four Elements Trainer

Witch Hunter

Insexual Awakening

SexNote

Imouto! Life _Fantasy

Quickie: A Love Hotel Story

LonaRPG

Teaching Feeling

Breeding Farm

Out of touch

But in my case I like those for stats management and stuff like that.

For story what I would recommend is (those are in order from best to last):

Out of Touch!

Love & Sex Second Base

Summertime Saga

Paradise Lust

For RPG puzzle and 3D as well as a very good story I recommend:

Lust Epidemic

Treasures of Nadia

The Genesis Order

In exactly the order I said them as they are part of the same story!