They are not exclusive, you can have both crit and highest magic level.
The only way to get critical is by:
- Imbuing a weapon with critical chance (10% chance, 50% extra damage)
- Conjuring Wand of Darkness, as a sorcerer: (10% chance, 50% extra damage)
- Using Cobra Wand (sorcerer only), which has: (10% chance, 35% extra damage)
- You can get 18% critical chance in a creature if you add LOW BLOW as a charm rune (only works for 1 creature)
Since most wands/rods have 2 imbuement slots, you can still get +4 ML on the 2nd imbuement, and wear a full ML set.
That means you don't have to choose between critical or magic level, just go with both.
For the set, check: https://www.tibiaqa.com/14337/what-are-highest-dmg-output-possible-items-for-ms?show=14337#q14337