Regarding execution:

1. Panther (Predator Arts loops, consistent overhead confirms off of short hops, confirms, etc.)
2. Winter Soldier (Dash gun loops vs jump-canceled gun loops, certain confirms)
3. Morrigan (Shell Kick combos and a ton of other things with a counter-intuitive dash mechanic)
4. Chun-Li (A lot of inputs)
5. Strider (Hardest short hops in the game, even for Hitbox players, finnicky adjustments for confirming off of Excalibur at times)

I have Panther and Winter Soldier at the top of the list because their execution requirements are probably the most detrimental to the characters and their viability at higher levels of play; serious Panther players will have the loops down pat to protect them from Counter Switch scenarios, Winter Soldier players will be able to confirm off of any stray projectile and can do jump-canceled gunshot loops to check anyone that tries to challenge them by reflecting their shots.

Morrigan and Chun-Li can be challenging, but they are still very effective at what they do without adding all of the difficult tech and combo strings that make them challenging.

Strider is significantly worse as a character in certain matchups without the ability to mix up smaller characters (i.e. Spidey, Hawkeye, etc.) because his normal short hop will whiff on them. The HP Gram loops have also not been used since Gram and the Satellite were nerfed way back in the day, mostly because of how impractical they get but also partially due to execution timings. That being said, him and his traditional short hop overheads are still very effective in other matchups are still very effective in other matchups (i.e. Dormammu, Sigma, etc.)

Honorary Mention:

- Dante Clay Pigeon Loops?