I relate the most to Lucca, via her deliberately rational mindset, her intuitive objectivity, her particular brand of optimism, and to a lesser (but still important) extent in her concern for those laid low by the many injustices of convention. The game writes Crono as the nucleus of the party, but I think it's Lucca who really brings them all together with a team spirit and a sense of common purpose. Of the entire main cast in CT, she seems the least hampered by stereotypes, and therefore the most relatable of them.
I also strongly relate to Spekkio, Magil, and Ayla.
Spekkio really is “delightful,” if you can imagine that word being used as “full of delight” rather than “delighting others.” This is an important characteristic in my personality, and so I relate to him fervently. The setting for his delightfulness is also appealing: He's deep down a very just person, but on the surface he's a total shit. The good thing is that he's not mean about it. Instead, he comes off as more of an eccentric, and I like that. (“I AM THE MASTER OF WAR!!! Walk around my room three times!! Muah ha ha ha hah!”
Magil is so relatable to me because of the way he carries himself. His excellent composure, his elegance, his dry wit, his mystique. I think many of us can and do envy such traits in a character, but I'm one of those who can actually relate to them as well. Not Magus (nor Guile); only Magil. Magil's aloofness is thorough enough that, except for what is explicitly revealed in the story, Radical Dreamers tells you nothing about him. All the rest is up to the imagination!
Ayla, of course, is perhaps the most insightful, lucid, and undistracted person in the series (except when yummy frogs show up), and she has that vivaciousness that we all admire. I can relate to her love of life and her incredible knack for boiling things down to their constituent truths.