Frankly I think the familiars are closer to each other than most people given them credit for. Sure there are a couple overpowered ones (Dino in particular), but 90% of them are pretty similar.
Don't be misled by stats alone, you have to factor in what they can equip as well. Something that looks weak may be able to equip a strong weapon, and something that looks like it has no defense may be able to equip multiple defensive items.
I mean, I think the game can be beat with basically any familiar combination. Most will have trouble identifying the 'worst' familiars just because there is usually a redeeming quality that lets them work.
RPGs Beaten(106) Maxed(65), Recovered MMORPG addict Current: Suikoden Tierkreis, Ni No Kuni, Atelier Ayesha, Titan Quest, FF13-3