I've played all of them very extensively and know each one's mechanics and whatnot at an intimate level. Smash 64 was a great game. I mained Captain Falcon and fell in love with the game from my first falcon punch. I've been playing competitive Melee actively since 2009 but have attended tournaments as early as 2007, maining Link/YLink as a casual and Marth/Falco competitively. I have played Project M competitively from 2011-2015, playing Marth throughout all versions And Falco up to version 3.02 (RIP Falco PM 3.5). Although I shun Brawl as a competitive Smash game due to its horrible balance, I look back at it fondly as a casual sinking hours of boredom into the game. Smash 4, I think, is the epitome of the casual games. They stress its competitiveness, but the game has nowhere near the level of skill cap and technicality that Melee has. Regardless, the game is wonderful and I love to play it. I can keep up with competitive players of the game due to past Smash experience, but I look towards the game with casual eyes and take it for face value. In that game I main Marth/Lucina (mixups), Corrin, Robin (stfu I love Fire Emblem), Cloud, Dr. Mario, and Luigi.
There are three aspects of the smash game: 1. Technical Skill 2. Mental Skill 3. Metagame
Combine mastery of those three, and you will become a very good player.