Ah...The oft-debated question. Note, though, that the topic is "who is Red in love with," not "who would Red be best coupled with." Experience has oft taught me that you don't always fall for the people who would be best for you. Sometimes, conflict is bloody attractive.
That being said, I think that if Red has a crush on anybody, it's on Gobo. She's competitive with him, but I think mainly she just wants his attention. (It's also part of her nature to want attention, but I do feel that's the reason she focuses on Gobo.)
One of the best things about Fraggle Rock is that there really are unexpected layers to it. If you want to see it, it looks sometimes like her constant challenging of Gobo, or her mocking of Travelling Matt' postcards, is her way of screaming, "Notice me! Notice me!" Plus, there's the episode that shows Red gets jealous of the attention Mokey gets, particularly the attention from Gobo. Part of this, once again, is just Red's personality: she's just got to be the star of the show most of the time, and can't bear anyone stealing that spotlight, not even her best friend. Still, evidence can point to Red having feelings for Gobo, particularly if you want it to. If you watch Fraggle Rock and look for it, you can sure find it.
I admit, I kind of root for Red and Gobo. I'm a bit like her in many ways, and admit that I'd probably be attracted to someone like Gobo if I knew him. Wouldn't mean we'd be good for each other or even that things would work out, but I'd be doing or saying the dumbest (sometimes meanest) stuff half the time just to keep him looking at me. (Lord, I know. So junior high for a 21-year-old.)
Still, thanks to a certain Mokey-lover, (curse you, Byron!), I can't help but see a little Red-Gobo-Mokey love triangle on occasion. Can't help but root for Red, though. because I love her, and I can't bear the thought of unrequited love for her. (I've always envisioned Mokey being more devoted to her arts, anyway.)
So, anyhoo, here's my ridiculously drawn-out point: If Red loves anyone, it's Gobo.