I like Lena's content but it comes off as "be more of a whore"/"be more of a prude", while Ian gets to make more meaningful, intimate choices and bond with each character he has sex with. It's like Lena's only option for a relationship more on the nice side of things is Ian, and if the player isn't invested in getting them together, her only options are a bunch of assholes.
I see it a bit differently.
For me, Lena's content is the more meaningful and enjoyable of the two because it comes across as (1) knowing what she wants out of the flings or relationships in which she's invested time, and (2) satisfying the very defined desires linked with each of these flings or relationships. Her relationship with Robert progresses from average casual sex to satisfying a new kink; realising that she has complete power over a guy who wants a serious relationship, but knowing that she'll never give him that, leading to greater sex. With Mike, the sex was already great to begin with, because of the associated risks; add to this the fact that the very idea of getting the best sex out of another woman's partner has empowered her, whether one accepts it or not. I'm pretty sure that paths to relationships with Jeremy and Axel would offer plenty of great story and content; both for different but equally interesting reasons. A relationship with Holly would be excellent too.
The one relationship that I can't seem to get excited about is the Ian-Lena route. It just feels like they're two people who are friendly and civil with each other, who are generally repressing a part of themselves so as to not offend each other, and who are sort of role playing being "good" or principled individuals in each other's presence to earn credibility and respect. Relationships can be complex, but what I do know is that you can't avoid the tension when it's there. Being unaffected or sincere through those early stages leads to growth, more often than not, if the other person is compatible. Social common courtesy does not create attraction, especially if one is curious or hungry to experience and enjoy unexplored kinks, uninhibited sex, and basically just a genuine and carefree life.
I think that this mentioned situation is one that Lena is currently in. Sooner or later, she'll end up realising that she can't repress certain feelings, that there are certain kinks or lifestyle choices that she can't live without, which, in her case, seems to be having sex without inhibitions, and of course role playing being a sex slave of sorts to a dominant partner. I feel as though whoever can fill that void for her, plus meet any of her other wants and needs, will have the advantage over others. The one thing that I did like about Ian in the update, as it relates to Lena, is his conversation with Axel, and being given the option to come clean with the guy about Lena.