If I'm playing against the CPU, I stick with level 8. I find that offers the best balance between "challenging" and "not relying on frame-perfect dodges".
There are certain characters that perform like a Lv9 even at Lv8 from all my casual "sparring" with them, actually. Of course, they are a little bit easier to beat than their Lv9 AI but man are they annoying.
- That cape spam and roll grabs are so tiring to deal with. Not exactly hard to kill, just extremely frustrating to so.
- Hoo boy, their grab game is real. Also they won't hesitate in catching you with a Side B just because of the super armor.
- All they do is try to grab you at every given opportunity. It drives me insane when all they do is Power Shield and grab you. Oh, but...they won't do anything to you and instead just roll spam backwards if you stand still with a charged projectile like Thoron or Aura Sphere. It's weird.
- Hilariously strong in the hands of an AI. Still dies whenever we slap them.
Any counter character- Power Shields into grabs, while they also have a Counter to boot! Yay!
- They actually do Jab cancels and it's frustrating when they do.
- I'm only listing him here because he's Sonic.
Speaking of AI, there are AIs that are hilariously bad even at Lv9... This is taken from my experience when playing a mini-game called Journey with my friend as we fight (with team attack on) a 10 Stock Lv9 CPU with only 1 Stock.
- Just floats there and does nothing...Even there are free punishes on display. I'm serious.
- They seem to forget what Luma is.
- They always use their Monado Arts at the worst possible time. Especially Buster and Smash.
- They seem whiff a lot...maybe that's just me.
- Whenever they catch you with an Egg Lay they will always whiff TWO smash attacks. Namely Down and Up smash.
- They try so hard to spike you they actually kill themselves. Or get spiked themselves. Most often the former.
- Too new for good AI, I guess. The shenanigans Lv9 Ryu pulls are hilarious.
- Maybe just me, but they are the sandbaggiest of the heavies when played by Lv9 CPUs...
- They Side B a lot when off stage. They will actually fall for repeated punishes from the Side B spam.
...I think I derailed too much. But I spent like 30 minutes typing this so bah.