Um, how does Fighting qualify as Very Bad while keeping weaknesses in the acceptable range?
I think this is just a matter of slightly confusing wording, Aura Guardian. He was listing "Weakness to Types by Severity," that is, "Being weak to Ghost is acceptable, while being weak to Fighting is unacceptable." Then, from that info, he was proceeding to describe the Secondary Typing choices that keep weaks/resists closer to the "Acceptable" end of things.
Thus, his Secondary Typing choices (Poison, Water, Fighting, and None) all, in his opinion, maintain weaknesses that are acceptable.
Elec/Poison: Ground 4x, Psychic 2x (one doubled Very Bad, one Acceptable)
Elec/Water: Ground 2x, Grass 2x (one Very Bad, one Acceptable)
Elec/Fight: Ground 2x, Psychic 2x (one Very Bad, one Acceptable)
Electric: Ground 2x (just one Very Bad)
I'm noticing the common thread here is, "Ground is meh, we can work around it or just suck it up." I generally agree with that line of thinking, but I'm sure there are others who would prefer to simply mitigate it outright with other typing choices.
I don't think Poison is viable. I just don't. A 4x weakness to one of the most commonly-used coverage types in the game? It hurts Poison's viability a lot, particularly since that makes countering certain powerhouses
significantly more difficult (I'm looking at you, Mamoswine, Hippowdon, and Swampert). Remember--Ground-types will be immune to CAP10's primary STAB, and if you add in a 4x weakness to STAB Ground moves, it's only going to make things worse (Ground types would also resist the Poison STAB!). The Psychic weak is not a big deal, but doesn't help Poison's case. Resists to Bug and Fighting are sweet, to be sure, and Grass/Poison resists are nifty nifty (if not terribly special). I don't, however, see the point of being Toxic-immune; CAP10's purpose is to be a 'utility counter,' you whip it out when its target is in sight, and stow it away once that threat is gone. Unless you and your opponent play a massive cat-and-mouse game, there's no
need to have CAP10 shrug off nasties like Toxic--and besides, with the well-known prevalence of entry hazards, cat-and-mouse games are dangerous in and of themselves
regardless of Toxic-immunity. </endrant> :P
Fighting subtype gives three proven-useful resistances (Dark, Bug, Rock) that reduce the effectiveness of common moves, common pokes, or both. True, it still loses a resist to Flying (though I doubt it would be possible to find a type that didn't drop at least *one* resist) and gains a weakness to Psychic, but that seems a fair bargain. There's also the offensive possibilities that Fighting opens up--a counter has to be able to hit decently well if it wants to succeed, right?
Water subtype is strong as well. Trading the admittedly-useful Electric resist for Water, Fire, Ice, and a double Steel resist? Yes please. The Grass weakness is roughly on-par with Fighting's Psychic weakness; yes, it's a hole, but it isn't a big one and I'd hardly call it threatening. Although GameFreak conventions mean little as far as CAP is concerned, a Water subtype would effectively guarantee Ice-type moves in the final spread, which is a minor plus. A solid subtyping, though IMO not quite as solid as Fighting subtype.
Bug and Flying deserve honorable mentions for consideration, but I think they introduce a few too many problematic weaknesses to be reliable. Each one mitigates the Ground resist, sure (Bug neutralizes, Flying immunizes), but each also drops a potentially-useful resist (Bug drops the Flying resist, Flying drops the Electric resist) which isn't bad but isn't good either. Both Bug and Flying add two nasty weaknesses: first, Fire or Ice respectively, and secondly Rock, which could be crippling. (SR-weak, and opening up avenues for Stone Edge and other nasty surprisies? I'll pass.)
I still favor
Electric/Fighting, but would have no problems with
Electric/Water.