The main differences between each FE character (somewhat proof that they aren't clones)
Marth: Sweet tipper spot, speedy, moderately decent recover.
Lucina: Middle tipper spot, but still legit female Marth.
Roy: Different Critical hit, Hilt sweet spot, neutral hold has faster cool down BUT does 1.5% extra damage if hit.
Ike: The heaviest outta the bunch, different final smash, similar neutral hold to Roy, but has farther hit spot. Has two recoveries (side b + up b). Pretty slow, but soaks most damage.
Chrom: Legit a mix of everyone. Awakening Aether does a critical if opponent has 100% or higher.
Robin: Magic over swords. Distance fighter, has gauge for each attack. Final Smash will crit if 100% or higher. Avatar character.
Corrin: Best jumper out of all, perfect for dodging high attacks. Different counter (dragon go rawr), and has different Final Smash. Avatar character.
Byleth: Uses something else other than a sword, very great for critical hits at early percentages, distance demon (thanks sakurai), vunerable to counters due to the slow startup, but deals MASSIVE damage if hit. Like Ike, but better.