(Welp, I didn't want to post another topic about this, and seeing as people haven't replied to this thread in a few months, I'll probably end up bumping it up. I'm new, and I wanna talk

)
About the whole 'breast' thing, I'm with 101 and Inquisitor, Medium to small is what I look for. I don't mind large breast from time to time either (maybe too large is a bit much though...)
I like how it's very imersive, in the fact that you have little to no control over situations at first (until you start really getting into the game). While I'm all for 'customization' when it comes to girls, there can be a slightly better approach that would feel like an actual accomplishment in the 'game' aspect.
In one of my favorite other adult games you can purchase drinks for the girls as gifts, each drink would have different side effects (such as increase or decrease breast size for a period of time). With the clothing physics in XStory I'm not sure how 'possible' that can be (I'm sure clipping issues would be off the charts!).
But if not, like many people mentioned earlier, it's best to just have a little in all directions, so you cover all the bases, so more people with different tastes still enjoy the game.
Another neat thing, since the conversations and interactions are a heavy key point in the games mechanic, if you befriend one, you could suggest, or say things like "I prefer girls with short red hair." To a girl with long blonde hair, and if she starts liking you, next thing you know, she'll have short red hair in a day or two. (Be kinda funny if there was a drink that magically overnight changed their race/skin color and slight eye shape, lol)
This could also become a neat system where the girls themselves have built in (hidden) gauges that determine interest and moods so that they can ask certain questions, and your answers might change the outcome of their appearance.