Buy a single deck if you want one specific Commander, want the cheapest possible starting point, or only one of the precons in a set appeals to you
My experience is that group hug is supported enough and variable enough that you can actually win matches with the strategy if youre good at politics, threat analysis, and deckbuilding
Looking at another difference, Modern has access to cards like Manamorphose, which generate a free spell and a redraw
The legendary also sees play in Commander, Vintage, and Legacy formats
Starter Decks Starter Decks are a great starting point for new players
Being able to make their own creatures lets them turn on the second clause of Deification without needing a third card in play