What is it that makes Chrono Trigger so great though? That's easy. Its combat makes active-time battles feel much more dynamic by having positioning matter in fights. The music is some of the greatest on the SNES too, with countless unforgettable tunes. Although it doesn't have the deepest lore, the story puts real weight behind every decision that players make, as multiple time periods can be altered by a single choice. However, its biggest strength is arguably how well-fleshed out its main cast of memorable characters is.
Crono is the game's silent protagonist. Akira Toriyama, the creator of Dragon Ball, designed the characters in Chrono Trigger, and that's incredibly clear when it comes to Crono. He's one step away from being a Goku clone in some pieces of art. He hardly has much of a personality though, instead serving as a blank slate onto which players can project themselves.
However, in a game with such vibrant characters, Crono's biggest weakness is that he's just another anime swordsman. He's combat-capable, sure, but he's the least exciting character in the game. It's clear based on later appearances and mentions that he has his own personality, but it hardly shows throughout the game. When all's said and done, he's just not that interesting.
Marle, who is later revealed to be Princess Nadia, is a healer with a crossbow and a sassy personality. She's usually strong-willed, except when the game keeps her out of the party. Sadly, once the story moves past her subplots, she's hardly a factor anymore. She has problems with her father, as all independent princesses usually do, and is also the canon love-interest for Crono.
In terms of combat, it's great to keep Marle around because hardly anyone else can heal as well as her. Her character is tropey and her role in combat is pretty standard, but it's important to remember these things are tropes now because they proved to be popular with audiences at some point in the past. At the end of the day though, Marle is just kinda boring.
Robo is a robot. He's from the distant future and is repaired by Lucca when the party gets shot far forward in time. He doesn't remember his purpose and agrees to help Crono and the rest of the party to pay them back for their kindness. He also debates many existential questions after learning the truth of his past, leaning further into the game's sci-fi elements.
Aside from having an absolute banger of a character theme, Robo is just a solid character all around. He has a touching backstory, strong combat capabilities, great dual techs, and no major weaknesses. He also works incredibly well within the already great battle system. He's an interesting addition as a party member in a genre that rarely stepped beyond traditional fantasy (at the time, anyway). Additionally, his friendship with Lucca is one of the best inter-party relationships the game has to offer.
Magus is one of the first examples of the "villain becomes a playable ally" trope found in many modern JRPGs. Throughout much of the story, Magus is an enigma. He's the person that cursed Glenn to become Frog, and is a powerful sorcerer. He wields a cool scythe and commands a great army. His battle theme and his duel with Frog are some of the highlights of an already incredible game.
On top of all of that, he has his own tragic backstory and his motivation for wrong-doing is more morally gray than would be expected of a typical JRPG villain at that time. His goals align with the party and, if he is sparred, he will join their efforts. He's a complex character, and very few villains in Square's library of games come close to being as interesting as Magus.
Ayla isn't as complex as someone like Magus, and not as emotionally compelling as someone like Robo. However, she's a character who's loaded with personality in almost everything that she does. She has distinct speech patterns, movements, combat skills, and her place in the lore explains all of that. She has the potential to be the highest damage dealer in the entire game too, and her ability to steal items is invaluable.
Ayla is driven entirely by a strong moral core that compels her to help Crono and his party defeat the ever-powerful Lavos. It is a bit of a mystery why she never uses the club that she carries in the FMV cutscenes, but that's okay. Sometimes, a character is just fun to have, and Ayla is definitely a unique party member in that respect.
Aside from Magus, Frog probably has the most well-fleshed out backstory of the entire main cast. Formerly the squire Glenn, he watches his closest friend die and is cursed to live life as a very big Frog. However, this didn't keep poor Frog down. He embraced his new form, making the best of a bad situation, and used his newfound abilities to become stronger. His new goal: kill Magus.
The story has Frog overcome his own self-doubt and guilt to eventually face the Fiendlord who cursed him years ago. If the player challenges Magus to a 1-v-1 with just Frog, it is one of the most powerful moments in the entire game. That all aside, he's also just a capable fighter and a great party member to bring along. Plus, his unusual speech patterns in the English SNES version are just endearing and fun.
Why is Lucca the best? Well, in terms of influence over the narrative, she serves a pretty major role. While Crono is the silent protagonist, her place at his side makes her the person doing most of the talking early on. She's loaded with her own guilt and self-doubt, and her scientific pursuits are an escape for her.
Lucca is devoted to helping her friends and family in any way she can, even though her inventions often backfire. As a combatant, her magical capabilities are only rivaled by Magus, and she also possesses solid utility in battle as well. She has a few weaknesses in combat, but those can be overlooked. When asked who the best girl in Chrono Trigger is, the answer tends to be Lucca far more often than not.