Just to put this out there but, personally, I don't find the Asari or any other species to be more attractive than human females. This coming from someone who always romances Tali, and even headcanons she looks like this.
First off, Salarians do get spoken of in sexual terms at least once.
Mordin: "Very awkward. Salarian skin tone apparently attractive by turian standards. Subset of krogan sexual deviants enjoy salarian flexibility. More cartilage in skeletal structure."
Krogan get talked about sexually over their large genitalia according to spam emails about some Asari leaving her lover for the krogan. Got Quad?
Hanar x Asari porn.
Asari have mated with vorcha.
Turians have flirted with quarians.
Batarians love slaving human colonists, don't tell me there isn't sex trafficking going on there.
Fornex.
I could probably go on but my point is that every species bangs every other. Even the damn varren are getting some action, apparently. We all suspect Kelly of this, don't we?
So I'm not really sure where this agenda of "only Asari are most wanted, humans are ugly" comes from. I will also point out theres at least two moments in the trilogy that I can remember where someone has NO INTEREST in Asari. The salarian at the bar had to be pressured into seeing something attractive about them. There was a krogan that shrugged off the thought of being with one for being too squishy.
In short, it seems to be much like the real world. Some people like them, some people don't. As for why Asari have larger appeal than others might be because they're very sexual. They actively seek to... interact... with other species. So much so that in Asari culture being with another Asari is actually a stigma. So is it really surprised that the species that actively and progressively pursues and encourages interspecies relationships (can even have children with) are more broadly accepted?
If humans in general made it a goal to only be with aliens I imagine we'd be more embraced as well. Though even today us humans can't even fully embrace other humans if our skin or nationality is different. So yeah. Asari trump us on this one.
What makes you think turians find human women ugly or that Quarians are more attractive than Asari? These are huge generalization to make. Javik says a few things about the quarians, who are widely hated and treated with mistrust, and suddenly they're more attractive than Asari? As for their "impossible" figure, they're aliens. Big surprise if something about them is impossible to achieve on our standards. I wouldn't even consider their hips and waist to the be most 'impossible' aspect of them. The raptor legs are what I'd see as impossible.
Some people would argue that they find the alien males more attractive than humans. Aliens have exotic appeal for being, well, alien. Plus personality does play a role. If I played Femshep I'd prefer Garrus or Thane and not even consider any of the human males. Yet I don't find them attractive at all - they just have good personalities and I find that more attractive. Hell, Thane scares me but I'd rather be with him then be with Jacob. Which is funny since you make the claim that drell as the most sexually appealing... Lol. To YOU maybe. This is all heavily subjective.
To summarize: human women are not the ugliest and human males certainly aren't the most desirable. Never in all my playthroughs of the game have I ever felt this to be so in Mass Effect universe. Infact, given how much ME2 and even ME3 panders Miranda's ass I'd say that human women are held in pretty high regard. Which is, imo, another case of personality taking precedence. I might be able to find Miranda attractive if it wasn't for the fact that I find her personality deplorable. Hard for me to see the outer beauty when her personality rears its ugly head.
Different strokes for different folks. IMO you should NOT feel inadequate or ugly for playing the game as Femshep. I find it strange that you care about this at all, really. Shepard isn't there to be a model of sexual desire. Would you really prefer it if everywhere you went as femshep you had all the NPCs catcalling you and trying to get in your civies? I doubt Bioware would do that. Unless you're playing a male character, anyway. 