Digital Devil Saga:
Serph: 8.5/10. There's a limit to how good PCs like Serph can be, since everyone in DDS has the same skillset. That said Serph is at that limit. His stats are by definition the best possible; you decide what those are.
Heat: 3/10. Fighters in DDS1 were pretty bad.
Argilla: 7/10. Argilla has the most magic, which is the best stat: it means the best magic damage (i.e. best damage), best MP, AND the best magic defence. Her durability could be a touch better but because Magic affects MDef (as mentioned) it's not too bad.
Gale: 5.5/10. Gale's okay. Third in magic (= third best PC because :dds:), okay durability, doesn't have a crippling weakness.
Cielo: 3/10. Has a crippling weakness, and the stats aren't great anyway.
Pokemon Gen 2 Grass, Bug, Ghost, and Poison types:
I'm generally willing to assume the Sludge Bomb TM can go to a STAB poison user; it's not a highly-coveted TM for coverage. This helps a few people on this list, though does mean that using, say, a grass/poison and Tentacruel at the same time is less desirable.
Venusaur: DNR
Vileplume: 2.5/10. Sleep Powder is a great skill and singlehandedly saves a lot of pokemon here. Past that, Vileplume has bad speed and crap damage outside Sludge Bomb, so is a very inferior choice of sleeper.
Parasect: 2/10. Spore is more accurate than Sleep Powder, but it's later (Level 28) and Parasect is even slower. Bah.
Victreebel: 6/10. Growth/Vine Whip is a far more capable earlygame offence than what Vileplume offers, and the speed is better too. So's the attack stat when you give it Sludge Bomb. It adds up a lot.
Exeggutor: 4/10. It has an okay Confusion as its damage (beats Vileplume). Reflect is nice, Leech Seed is nice. Hypnosis instead of Sleep Powder (until high levels) isn't nice, nor is the speed.
Tangela: 2.5/10. See Vileplume, remix the stats a bit, take away Sludge Bomb.
Meganium: 6.5/10. Grass is a good attacking element. Why am I bringing this up now? Because NOBODY ELSE GETS IT. Meganium, however, has a Level 8 ~65 effective power grass STAB, so that's pretty cool for a long time, even if eventually outclassed by the likes of Surf. Reflect + Synthesis gets it past some tough fights, too. It doesn't have much status, though, so it's not a straight improvement over other grass options. Still... sure, best starter.
Bellossom: 2/10. See Vileplume, minus Sludge Bomb STAB. Okay.
Jumpluff: 7/10. Great speed! Sleep Powder, Leech Seed, healing = kill even most bosses provided they aren't packing ice. The damage makes it annoying to level though. I found it pretty awesome in FRLG and it's not that different in GSC on paper.
Sunflora: 2/10. It can actually launch grass attacks... but that speed... and that Sunkern stage. No.
Celebi: DNR
Butterfree: 4/10. 70 speed Sleep Powder and not much else. But hey, that's enough.
Beedrill: 1/10. Oh god. This was mediocre enough in RBY, but delaying Twineedles until Level 20? Really?
Venomoth: 1.5/10. Kinda like Butterfree... except joins underlevelled and Sleep Powder's at Level 42. Ugh.
Pinsir: 4/10. I have no idea how practical the bug catching contest is, but... eh, it's Gyarados available earlier (which matters), non-STAB Headbutt/Strength/Return and not much else (late Submission instead of shitty Surf). Just use a damn Normal if that's what you want.
Ledian: 3/10. It... has dual screens, and Boltbeam Punch, off okay speed and crappy stats otherwise. This isn't actually... that terrible. But certainly isn't good.
Ariados: 1/10. Slow, bad durability, crappy skillset.
Yanma: 1/10. 1% encounter? Fuck that. It's bad anyway! Non-STAB Headbutt off crappy stats outside decent speed.
Forretress: 1.5/10. Uh, trash stats until Level 31, and even then it's not good for much besides non-STAB Strength and blowing up.
Scizor: DNR, 4/10 Scyther yeah. Good stats, trash skillset, trash typing. Someone else who runs non-STAB Strength/Return oh boy.
Shuckle: 2/10. I guess... Rollout lets it almost kind of do something.
Heracross: 4/10. More non-STAB normal moves off good stats awww yeah why is this not actually an awful option. Also I really doubt it can sweep Karen given that her best if a Houndoom and it still likely won't have Megahorn by then anyway...
Arbok: 2/10. So there were a few pokemon I randomly fanned over due to design/anime appearance rather than in-game. Some of those (Starmie) turned out amazing, most of the rest (Persian, Dodrio) at least turned out competent. Arbok, though? No, Arbok is pretty bad, especially after RBY. STAB Sludge Bomb helps it, and the stats aren't total garbage, and it has 75% stun which works on grounds... but otherwise it's really blah all around.
Nidoqueen: 5/10. Good TM/HM list, average stats... eh, it works. I can't say I liked them in RBY (just use Clefable, better Special), but in GSC the standards are lower.
Nidoking: 5/10. As above.
Muk: 2/10. Kanto scrub with some usability.
Gengar: 6/10. (as Haunter) The stats and typing are nice, and between Shadow Ball/Sludge Bomb and Night Shade it isn't completely awful damage, and Hypnosis/Confuse Ray is decent annoyance. That said the sleep could be more accurate.
Weezing: 2.5/10. Doomed by a Level 35 evolution. It could have been useful otherwise, Weezing stats are pretty okay.
Crobat: 6/10. Great stats, confuse ray... offence is kind of iffy until Fly, though. (gym 5) I found it pretty great in HGSS but Wing Attack is a lot earlier there, and Bite is earlier/physical.
Misdreavus: 3/10. You can use this against Ash... uh. Well it wrecks the Snorlax. I guess that's worth something.