Can anyone compare Agenda and Standard Notes?
Agenda puts the focus very much on dates and events. In a professional environment most notes that people almost always are related to a certain event (meeting, conference, etc) and/or associated with a certain date (release date, deadline, etc).
Most note taking apps, including Apple Notes, don’t have much of a concept of dates beyond creation date, and often sort notes simply by the last edited date or creation date. Agenda makes dates and events first class citizens, allowing you to associate your notes directly to the dates and events they refer to, and also importantly, keeping them consistently sorted with these as you edit them. That’s the biggest difference between Apple Notes and Agenda I’d say.
Standard Notes is different from Apple Notes. The OP didn’t ask about Apple Notes.
indeed 
I was asking to see difference, in therms of sync, storage, features etv, not with Apple Notes but that one
Ah, I assumed with standard you meant “the default notes app”, apologies. Alas, I have no experience with Standard Notes, but others might chime in.