It really comes down to an individual's preferred meta. Going chronologically, while in many aspects it is the most simple of the games, it still has a fairly active scene (which I know little of so I won't try to explain parts of it), next there's Melee, which is what got Smash as a series into being a competitive game. The advanced techniques can create mind-games in a unique way, and while extremely accepted as the main competitive game, isn't exactly everyone's cup of tea. Brawl's meta is Meta Knight, unless of course he's banned from a tourney. Project Mayonnaise, is for people who want Brawl's content with physics similar to Melee, with a few extras thrown in, and having an alternate meta to Melee, it is always a popular pick in the competitive realm. Most recently there is Sm4sh, it's engine finds a balance more in between Melee and Brawl's paces, with it's own unique meta, which expands with the added content(characters and legal stages), that and it is fairly balanced in it's roster, so most the sizeable cast is still seen fairly commonly.
