Smell is extremely important. I have that issue with my husband's girlfriend. I like her, she's really into me and we've had a few threesomes but while she doesn't smell BAD, I just really don't like her scent so I've stopped sleeping with the two of them. I know my husband is bummed, he was really into the threesomes (of course) but I just can't bring myself to go down on her and feel it would be a dick move to just have her do it to me without reciprocating so it's better to just not do it all together.
On the other side, I have often been told that I smell very good and suspect that I may be one of those people that have strong pheromones. I'm a big girl, but have never had a problem with men not being attracted to me, even (and often) when I am not usually their type. Without fail, they all mention that my smell was a not insignificant part of their attraction. Of course, this is all conjecture and unsubstantiated hypothesis, but I find it interesting nonetheless.