Junko. Junko is the one who can show the difference between Nagito and Makoto's luck.
Junko is the smartest person on the planet. Her main ability is to analyze and predict everything, events, people, powers, machinery. Her brain is literally OP.
However, she isn't impressed with Nagito. Nagito's luck doesn't protect Nagito from Junko.
Because Nagito's luck is actually pretty easy to analyze. The 5th trial of the 2nd game, the students used Nagito's luck as real evidence in finding the killer. If Nagito's luck was actually strong, it wouldn't have been conquered by the students.
Junko, however, is in an entirely different league of brain power than students. She analyzed and predicted Nagito's luck so she was never in any danger of losing to it. Actually, Nagito, with his luck, did set out to stop Junko, twice. First time he failed, Junko brought Hajime with her and the second time, Junko looooooowwwwww diff brainwashed Nagito. Nagito than became a servant of Junko, spreading malice and ill intent across the world, in his own way.
But... Junko could never pull off the same thing with Makoto. Makoto's luck can't be analyzed and predicted by Junko by the very nature of his luck,
as told by Junko's lips here, 0:42.
Junko likes Makoto, not for anything other than Makoto's presents can disrupt any Junko's plans, as no one on earth can do the same.