To me, Asuka seems like Tomoko's "Girl Next Door". There's a lot of sexual tension there, but they still seem to be on different wavelengths. They haven't seemed to reach a more intimate level of understanding beyond distant acquaintances yet, despite them both trying to close the distance.
Yuri kind of already acts like Tomoko's girlfriend, but is too awkward to even realize she's doing it, and probably doesn't even realize how interested she actually is in Tomoko. They're both "loners" and have the potential to bond over their social awkwardness, but that's also a deadly combo, since they'll probably end up stumbling over a lot of miscommunications because of it.
Tomoko and Nemo have a lot of chemistry and seem to have the most natural relationship out of the three pairs. They have shared interests, the longest history, and seem to inspire each other and help each other grow. For these reasons, I personally think they have the potential to be one of the cutest possible pairings, but their relationship is also the one that most seems to lean toward "friendship" rather than "romance". Their personalities play off of each other really well, but that's also probably partly due to the fact that it feels like in comparison, the sexual and romantic tension in Tomoko's relationships with Asuka and Yuri seem to be somewhat lacking in her relationship with Nemo.
I don't really remember where I was going with this, but I guess that's my two cents on the pairings that no one asked for. I guess the point is that all three pairings are good. They just have different flavours to them, or something like that.