Orlandeau -
+ A great evasive frontliner with high damage and utility; Flexible secondary skill slot
- Poor status resistance options; Defensive gear only gives HP; Requires item based healing from allies

Celes -
+ Powerful mage with great defenses and physical prowess; Runic provides defensive support for the team
- Ribbon is a relic; Runic doesn't stop all magic; Runic prevents normal magic from allies

Shadow -
+ Throw bypasses Runic; great magic pool; Can steal; Free physical block & counter w/Interceptor; Attacks inflict status
- Poor equipment pool; Ribbon is a relic; Interceptor isn't reliable

Farris -
+ Mix & Blue Magic provide reliable and powerful buffs; first action via equipment; great equipment pool; is a pirate
- FFV characters don't have downsides. >: I

Last slot is extremely hard, going to either Zell or Aerith, but, ultimately . . .

Aerith
+ Party invulnerability; Final Attack Phoenix; KotR damage is obscene; Materia gives her peerless versatility
- Great Gospel requires a full limit gauge; fairly frail

Zell brings better (non-Knights) damage, defense, and on-demand party invulnerability to the table, but FF8 Phoenix is extremely unreliable for preventing party wipes, and he is limited to how many command actions he can have at a time, both of which push Aerith ahead.