I'm echoing Delver here:lil more discusion on stunky and ponyta please
Reliable recovery is debatable as, like Hawkstar said, Morning Sun is nerfed by Sand and Hail. I'd add SPEED as one of the main selling points for Ponyta (BST in general). Speed 19 is very appreciated when Murkrow and Misdreavus are in every match and the fact that neither one of them resists its main STAB is very appealing (Murkrow being weak to Wild Charge is a bonus). Weakness to Stealth Rock and the fact that it gets crippled by the thing it's meant to counter (Stun Spore/Spore) or heavily damaged (AncientPower Lileep) is a drawback heavy enough to let it be out of A, in my opinion. However, I'm not opposed to see it in A as a very skillful player can let it shine regardless of its weaknesses.For reasons I've detailed in an earlier post I think Ponyta is at least B. I think the main thing it's got going against it is a mono-fire typing which makes it weak to 2 very common attacking types in ground and water, as well as the omnipresent rock. Regardless it's still a powerful mon with good coverage reliable recovery and a very strong STAB.
Stunky is, to me, a C. It has one use only: kill Ghosts. I'm not sure if it can KO Misdreavus after a burn but I find Murkrow, Vullaby and opposing Misdreavus to be far better counters to Ghosts; the only other "common" ghost I can think of is Frillish who can also burn it missing the whole point of ghost-trapping (no good player will switch out on Stnuky, ever). Its only weakness is very exploitable in the meta and cannot stand a chance against many threats because it often carries Dark-moves only, meaning its Poison-type is not useful at all, not even to absorb Toxic Spikes because they are uncommon. C-rank IMO.