Walkthrough:Chrono Cross/Zeypher/Save Kid or To Not Save Kid
Here are the two options and the recruitable characters you can get if you choose each one of them (to save Kid or not, after she's been poisoned at Viper Manor).
Korcha isn't terribly awesome, but Mel has a double-tech with Kid if she's recruited. Razzly is very decent, though...her last tech RazFlower is just pretty difficult to get. Two outta three ain't bad. People with a conscience will choose this path. Saving Kid is probably the easier route, as one obtains the Astral Amulet earlier and can steal Moonglasses from an upcoming optional boss (rather than her dropping them).
Most people choose this path because of the last character, Glenn. Not only is he one of the most powerful person in the game, but he has a double-tech with Serge called X-Strike (like in CTrigger). The other two probably won't be used, but man, Glenn's a catch if you pick this path. Definitely worthwhile to go this path, moreso than the other if you don't have any pangs of guilt for not saving Kid. Also, since you're not required to go to Hydra Marshes yet, y'can wait until the 16th star and get trap Tornadoes from the Wingapede boss (thanks to Guillaume Audet for this tip.) YOU CAN STILL RECRUIT KID LATER IF YOU CHOOSE THIS PATH. Choosing this path means that Kid won't join the party until very late in the game. She's not missable per se (unless one purposely doesn't try to invite her or do any sidequests pertaining to it), but it's an awful long time to wait nonetheless.