For PvP: Lower level/High %? Or vice versa?

There's a ton of nuance to this that there isn't really a cut and dry answer. Attack is weighted much more heavily in CP calculations than defense and stamina, which has led some people to favor lower attack IV Pokemon for PvP because they can be powered up more without going over the CP cap. This means that those Pokemon will be higher leveled and subject to a higher CpM, potentially resulting in higher stats.

For example, your perfect Sceptile's attack will be as follows at L33:

(223 + 15) * 0.74976104 = ~178.44 floored to 178

Compared to your imperfect with 9 attack:

(223 + 9) * 0.7731865 = ~179.38 floored to 179

Essentially, due to the imperfect Sceptile being influenced by a higher CpM value its attack stat and potentially other two will end up higher at the given CP compared to your perfect one. CpM multipliers also vary from level to level much more in the lower side of the level cap than the higher side. The L33 CpM is 0.74976104 and the L37 CpM is 0.7731865, less than 0.025 difference in multiplier. A 4 level difference in the mid-20 range can see double that difference, meaning for Pokemon that hit the CP cap in those levels it may be more beneficial to use one with sub-optimal IV's. Again, there's tons of nuance here and because every Pokemon has different stats there's no clear cut answer on which IV's to shoot for.

There's something of a cost/benefit factor to consider as well, especially when you approach the higher end of the level curve. The candy/dust cost to power up from L33 to L37 is 72/60k. Is the extra point worth all that extra dust and candy?

CP is based on three stats: attack, defense, stamina

Each of those stats is based on three variables: base stats, IVs, CPM (level)

The separate variables don't specifically matter. If different pokemon with different IVs at different levels have close to the same calculated stats, and they have the same moves, then they would perform close to the same.

The calculated stats, and their ratio to each other while remaining under the CP limits are important. Generally speaking, a lower attack IV can allow for more defense and stamina IVs at about the same CP. This would cut the calculated attack stat a little, but provide a higher increase in combined defense*stamina.

There are spreadsheets available that can compare the calculated stats of different IV and level combinations to see which has the best powerup potential for stat products within the CP limits. GamePress will probably release a PVP calculator at some point to do the same.

All of the above is good, but there's also the issue of what the ideal stat combination is. Should PvP stats (base + IVs) be balanced, defense heavy, stamina heavy, attack light, or what? That's still an open question AFAIK. Answering it will give us all a lot of help towards the ideal choices for PvP pokemon.