the main counter question is: "for which purpose?"
PVE: it just needs to be one speed about ur target, which is known before u fight ur oppponent.
PVP: the faster the better, in pvp speed is king, there is rarele a situation where u win because of power, mostly u win because of control, and that means, faster better.
BUT: it depends what ur team is about, but frakly in general spoken, faster ist mostly better (97%++)
But in todays setup there are some defaults it seems: primal cry, direhorn, swap teams, anub idol(very strong pet in my opinion, i dont play it btw for some special reason
it seems that, with the right starter/opener pet and right swapping u can win a pet battle even if u were considered to loose at the beginning by plain pet score, but this is what scores good pet pvp battle player