If you're looking for a character that covers Luigi's weaknesses, check characters like Sonic, Wolf, Link, Sheik, Roy, Cloud, or Diddy. These characters excel at the neutral game and aren't at as clear a disadvantage as Luigi when you lose advantage. Many of these characters also have effective zone-breaking potential.
If you're looking for someone to pick up that plays similarly to Luigi, try Mario, Lucario, Wario, Ken/Ryu, or Incineroar. These characters have great combo games or a lot of comeback potential but are just as polarizing to play as Luigi--except for Mario and Wario. Mario is fairly balanced, but trades less powerful combos for more versatility. He is still a combo-focused brawler like his green brother. Wario, on the other hand, has a fairly good neutral, but his comeback factor is on a timer (Waft).
If you're looking for the opposite of Luigi (lolMario), pick a zoner. Simon, Marth/Lucina, Young Link, Olimar, R.O.B., and Rosalina seem to be some of the best or most popular zoning characters. Each zoner can feel a little spammy in their own way, but you can become a powerful trapper by carefully choosing what you're going to zone with and when.
Don't shy away from top tiers, because their metagames have advanced further than other characters. This makes picking one up relatively easy, even if the character is complex, because there are tons of sources to help you learn them.
Hope your secondary search goes/has gone well!
