The only levels that matter for CPUs:
Level 3: Fully functional recovery abilities- will make all attempts to recover before dying.
Level 6: Stops any and all defensive tactics- will "always be after you"
Level 8: Mastery of Power-shielding, begins to attempt to block your attacks.
If you're going to practice against CPUs to get better, only practice on level 3s- they recover well, and that's all you need them to do. Their only real use is to try out combos/setups in a 'normal' setting- training mode fails simply because the option of slowing time down is a trap and your attacks don't get stale.
If you practice too much with level 7-9 CPUs, you'll fall into being able to read their reactions well, but be completely clueless in a 'real' match, since real people act completely different from CPUs. Practice with caution. Personally, I practice on level 3s only when no other options are available. Even crumby 'real people' are better practice. Unfortunately, I end up doing this a lot. 9_9;