Interactive as in friendly? I'd vote for corydoras but I'm prejudiced, I love them. Guppies are quite tame and always out for food so they suck up really good if they think you're a softie in the feeding department.
Interactive as in terrorizing a tank? One of those red-tailed sharks OR a single tiger barb or green barb(in a school they're great though, no problems). My daughter got some zebra danios and they were so aggressive we had to give them away, they were after the guppies, the cories, anything that moved. Yeesh.
No clue why.
Interactive as in "I know you're in the room, now come over here so I can show off to ya?" Definitely a Betta! Mine does that all the time. Guppies will put on a huge show if they think you're going to feed them, then they ignore ya
, but my Betta will sometimes just want company and acts genuinely happy to me when I enter his room space.
I find my tetras tend to act more like what I think are typical fish, keep to themselves, dart out for food but don't care if I'm there or not. They tend to keep to themselves too, while the guppies and corydoras are into everything and anything, always curious. Hope that helps! I hear goldfish really get to know their masters, koi too, but I don't have tanks big enough for them. (besides how they remember you with supposedly only a 3 second memory is beyond me)