Well, shit... I've been lurking on here for a while now and THIS is the thread that ends up being one of my first responses.
So here's the issue: sexuality, like many other aspects in our lives, is a spectrum. It is not, nor will it ever be, as simple as a ternary straight / bi / gay answer. Adding to this is everyone having their own opinion on how each sexuality is defined and wanting to either have an absolute answer, declare their answer is the correct one, or otherwise get confirmation they have it right in order to clear up any doubts and/or insecurities.
The problem with these thoughts is they'll very often focus too heavily on the specific sexual acts depicted and completely ignore sexual attraction.
Take pegging for example (usually Female penetrating Male with strap-on, for any unaware):
While some would consider it gay simply because the male is the one being penetrated, it's not really that simple, is it? It's still a hetero couple. If either were gay, it's unlikely they'd ever get to this point with someone they weren't attracted to. This is also ignoring non-con which is an entirely different issue.
On the note of Futanari characters: this is a fictional gender*, so it doesn't exactly fit into the hetero / homo spectrum. It doesn't help that Futa characters are almost exclusively using feminine pronouns - not saying this is wrong, we don't exactly have a commonly accepted pronoun for a gender that doesn't exist.
*Yes, people can be born intersex, but, to my knowledge and the admittedly brief search I've done online, there has never been a reported case of someone being born with both sets of genitals being fully functional.
At the end of the day, there is no true answer; people are going to like what they like and dislike what they don't. I didn't really think there's a need to get so caught up in attaching a label to it. Just be comfortable with your own sexuality and try not to put others down / insult them simply because they don't share your preferences. (Not saying anyone in particular is; just making a general statement)