Without making this into a debate about what's more "prestigious" (ECNL vs EA/MLS Next), the highest league for the boys in SoCal would be:
9 and younger - flight 1 SoCal League
10 and 11 - EA
12 years and up - MLS Next
Clubs choose ECNL path (Pats, Slammers) or EA/MLS Next path (TFA, City SC, Albion, Strikers, Liverpool, LAUFA).
It seems as though the most of the "big and best" clubs have chosen the EA/MLS Next path and since majority of the parents see it that way, it's become the de facto truth (and the fact that MLS Academies compete in MLS Next).
On the girls side, I think ECNL > GA but location/age could sway it the other way. In GENERAL though, if college soccer is the goal on the girls side, ECNL is very well tracked by college coaches and scouts and thus highest level girls play in ECNL.