The difference is that most of the MCU style has migrated over to the comics so in many cases they represent the current style. SLJ Nick fury, Hawkeye without the circus costume, Thor look, etc
Depends.
Some have merged, some others have a different universe.
Like I had mentioned before.
Guardians of the Galaxy currently has 3 arcs going on.
1 Guardians of Infinity
2 Guardians of the Galaxy
3 Marvel's Guardians of the Galaxy (related to the cartoon and MCU).
Both use similar designs but with some distinctions.
Example.. characters in guardians of the galaxy constantly change suits or details (rocket's suit change from time to time, same with his armor or space suit or guns, Marvel's MCU comic always have the basic weapons and the same identical look in ALL the series)
Not too sure about other Marvel characters, but I know that Iron man constantly changes suits. And the new arc of "all new avengers" have him completely different from your usual (including him being relatively "broke" and who had to sell his Avengers tower and Sam Wilson taking over the Captain America mantle).
Then you have 2 main universes.
Amazing and Ultimate (white nick fury vs black samuel jackson nick fury)
MCU seems to be a mixture but mostly using Ultimate's versions.