If I had to choose it would be Unridden, it's a little more plausible they would have trained wolves fighting in packs for them.
I'd choose to have Thunderwolves scoured from human memory, it crosses the fine line for me between fantastical and hilariously ridiculous.

But in truth, you'd need to include both preferably to satisfy all SW players.

I would go with the real old school approach, no cyber- or mutant-canines at all

no, but seriously, why not try this stuff out? put both in the army list, let people play a couple of games with them and then let us return to the discussion. Maybe it will have cooled down a bit by then. I am quite surprised at the level of erm...emotional involvment that has gone into the discussion of this very point. Although this seems a rather minor point imo. I dare say, let it rest for the time being. Let us think about how the SW list works in general and return to the battlepets a little bit later.

cheers

sanjuro