I like Lena as a character, but I do think that her storylines overall (at least the straight ones, so far - that could change with Axel and Seymour routes) aren't anywhere close to being as interesting or exciting as Ian's are.
Similarly, I find Ian more interesting a character then Lena is; or rather, I feel like his personality is a little more fleshed out and nuanced then hers is at this stage.
To me the sex scenes wouldn't be anywhere near as hot if Ian was just some faceless/nameless guy.
I find Ian's sex scenes to be much hotter than Lena's, i think that's due to the variety of women he meets, you've got bossy ones, clingy ones, innocent ones, flirty ones, it's great.
Lena on the other hand has stalkerish LI's and creepy asf future LI's, Seymour may be interesting in that whole "submissive woman, dominant man" angle, but we'll have to see.
Edit: Oh, i guess there's Mike and Jeremy, so there's that.