Easiest way i found to get this achievement is to get to Zangief with anyone... Lose to him and pick E. Honda... Stand still and just do the 100 Hand slap by rapidly pressing any punch button... Do this for both rounds, if you get hit (most of the time you won't as long as you're constantly doing the 100 Hand Slap move), die and try again.
Dhalsim is also pretty easy to perfect. The examples provided below are assuming you are on the left side of the screen:
M. Bison: Psycho Crusher (Charge , then + Any Punch)
E. Honda: Sumo Headbutt (Charge , then + Any Punch)
Blanka: Rolling Attack (Charge , then + Any Punch)
Either spam these moves or you can try to hit crouching heavy kicks on Dhalsim until he is KO'ed. Zangief can also be perfected if you jump up and down in the corner and heavy kick him as you're coming down. If you use E. Honda you can mash the punch button quickly for Hundred Hand Slap and Zangief should walk right into it. This may take several attempts as well as some luck but since you will have to play Arcade mode multiple times you will more than likely unlock this naturally while going for Perfect World Champion.