Design wise, Arcanine is better in my opinion.
Competitive wise, Arcanine still wins majority of the time. 40% of Arcanine run Choice Band, that means Arcanine will have ExtremeSpeed. Since nobody uses HP or Def EVs (unless it is the 40 HP one). ExtremeSpeed deals 75.95% - 89.69% to no HP / Def Houndoom, so after SR, it OHKOs (the 40 HP one has a 90% chance of OHKOing). Life Orb set has a 20% chance of OHKOing as well after SR damage. Then, there is the wall Arcanine variant, it does carry Hidden Power Ground that 2HKOs, but Houndoom also 2HKOs. So, Houndoom would win due to higher Speed.
Yeah... :x