In Chrono Cross, the Yellow Element is the earth to Green's wind. Yellow spells are full of earthquakes and thunderstorms, and the characters associated with the Element are all down to earth in some ways - sometimes literally, in the case of a certain mushroom.
Green Element enemies are quite populous in Chrono Cross, so having a powerful Yellow character around is a good idea, as their attacks will be super-effective against them. The roster of Yellow characters is largely geared towards the physical stats, so here, we're really just picking the character who can clobber your enemies the hardest.
8 Sneff
Sneff is an "Aged Illusionist" and doesn't deserve to be able to call himself that. You'd think someone who knows magic would have a good magic stat - nope. He has a very bad magic stat, which is such a shame because his Element Grid is pretty darn nice.
In fact, all of his stats are bad. He's going to be taking a lot of damage and not dealing enough to make him worth recruiting, and his techs are even worse. HP Shuffle is unique, but in that disappointing way that makes it not worth using.
7 Poshul
Despite how adorable and likable (okay, some people find her utterly annoying) Poshul is, she's just not too great in a fight. You'll find out quickly that she has pretty great physical stats but her magical stats are awful. Her magic stat is on the floor and her Element Grid isn't that much better, though she does have a nice amount of early-level slots.
The one upside that Poshul has is that she's around for most boss fights in the game, so she can get a ton of stat boosts in between thanks to the way leveling up works in Chrono Cross. While this will never make her a decent mage, she can be a more-than-serviceable physical powerhouse if you put the effort in.
6 Funguy
As a physical attacker whose best unique techs are magic attacks, Funguy suffers quite a bit. Add to that middling stats across the board and the only remarkable thing about Funguy is his appearance. Seriously, a mushroom who wields an axe?
There really isn't much to say about Funguy, especially in praise of him. He has a lot of level one and two Element slots, so that's something, but the tail end of his grid is so abysmal that it's not worth talking about. He's a physical attacker who pales in comparison to the many physical attackers on this list.
5 Mel
Despite being a child and not a magician, Mel is the Yellow character most likely to be called a mage. And that's just hilarious because she's not very good at it. Her Element Grid is only above-average compared to the better mages in the game like Leena and Riddel, and her magic isn't actually that good. It's just good for a Yellow.
There is one thing she has going for her, though, and that's the Snatch tech. This is like Kid and Fargo's stealing abilities that let you nab items from enemies. This automatically increases her worth, but the thing is both Kid and Fargo are better at the task, and you won't be able to field a team of all three until New Game+, anyway. By that point, team composition doesn't really matter.
4 Viper
Despite being quite an important character, Viper is a bit lackluster in battle. It's cool to have him around, but he's a slight hindrance to optimization. Firstly, his stats aren't too good - his strength is high but everything else is disappointing.
Secondly, Viper's Element Grid is pretty abysmal. He has very few slots of any level, so he's not going to be one of your utility casters. And finally, his ultimate tech is a total letdown, providing only a big defense boost to Viper himself.
3 Norris
Norris isn't bad, but he certainly isn't great. While he has some great things going for him - such as a level five tech that does a ton of damage to all of Norris's enemies and above-average speed, his combat stats are pretty bleak.
He's ostensibly a physical attacker, but his defensive stats leave something to be desired and his good Element Grid is wasted on a low magic stat. It is important to note, however, that Norris uses guns, and it's possible to acquire an extremely powerful gun without the use of a Rainbow Shell once you recruit Starky.
2 Zoah
As a Yellow character, Zoah is basically Viper, but better. He's a physical attacker with no magical aptitude whatsoever, but his stats make him far more capable of the fighter role than his boss.
Viper does have a lot of level one, two, and three Element slots in his grid, so he can be used as a utility caster with status healing items and status effects, but he's better off picking a single enemy and wearing away at them for the rest of the battle. In fact, all three of his unique techs are single-target damage techs, so that seems to be his ouevre. Oh well, he's good at it.
1 Leah
Guile ended up being one of the best Black Element characters in the game and he's a pretty oblique reference to Magus from Chrono Trigger, who woulda thunk that the same would be true of Leah, this game's reference to Ayla?
Leah has fantastic physical stats, with huge HP and strength levels. She is easily the best Yellow on the roster when looking at how much damage you want to put out there, and she should be heavily considered if you're going up a tricky Green boss. Just be sure to have some healing on hand, because her abysmal magic resistance means that even weak enemy spells will shred through her large HP pool.
It's also worth noting that she has a really great Element Grid, so while it's absolutely inadvisable to make her a caster, she can make do with utility spells aplenty.