Miicharacters.com helps a lot. Though to download them you will need a 3DS or Wii U to scan the QR codes & an amiibo to transfer over to Switch. Some more advice: copy them from amiibo in the Switch's native mii maker app, not SSBU's built in mii maker. Switch version gives access to more hair colors to update some miis. Some of my personal favorites:
-Heath Ledger Joker=green hair+purple butler suit (any style)
-Iron Man=Red hair+Samus Armor
-Spider-Man=Tracksuit (red)
-The Count from Sesame Street=Vampire Garb (black)
-Saria=green hair+Link outfit (or default swordfighter) (also I altered the hairstyle on the one found on this site)
-Malon=Orange hair+Wild West Wear (white)
-Cia=white hair+Viridi Outfit (Ashley outfit if you want a more accurate weapon but I don't the tradeoff's worth it)
-Aladdin=Toad Outfit (purple)
-Captain Hook=Pirate outfit (red)
-Captain Jack Sparrow=Pirate outfit (brown)+pirate hat
-Iwata/Reggie/Miyamoto/Sakurai=Business suit
-Naruto=Ninja suit (orange)+ninja headband
-Goku=Fighter Uniform (orange) (also I made his hair light blue but that's optional)
-Misty=Orange hair+Saki Amamiya Outfit
-Red Power Ranger (2017 film version)=Cybernetic Suit (red)+Captain Falcon helmet
-Aqua from KH=light blue hair+Chrom Outfit
-Megatron=High Tech Armor
-Roll=Wild West Wear (red)
-Deadpool=
https://www.youtube.com/watch?v=FW__1VOMc68 for the mii+Yiga clan outfit (I swear they put this in just for the sake of Deadpool miis)
-Fighter from Final Fantasy 1=red hair+Black Knight Armor (since other knight armor got cut)
-Dixie Kong=Tiny Kong mii (it looks better)+Monkey Suit+Dixie Kong's hat
-Blaze the Cat=light purple hair+Protective gear (dark purple)