X-men: X-Men, X-Men 2, Logan - No need for Origins, Wolverine or First Class or Apocalypse
Not linked: Deadpool - I didn't enjoy it that much, some great bits of humour ruined followed up with jokes that don't land. TJ Miller is awful, every scene he was in dragged.
Marvel Cinematic Universe: Recommended - Iron Man, Captain America, Avengers, Iron Man 3, Captain America Winter Soldier (2), Civil War, Doctor Strange, there's not really a bad film in the MCU although most are skippable. There's a real drop in quality between Iron Man and its sequel. I can't really recommend the Thor films, dull as dishwater.
You can watch Daredevil and Jessica Jones after Avengers.
DC: Man of Steel, Batman vs. Superman (Don't bother with Suicide Squad)
These are recentish standalone films based on comics/graphic novels that I recommend:
Dredd
Kingsmen
Snowpiercer (not sure if it's even out im the UK, I watched it on Netflix when the region switch cheats worked. It was fantastic until the final scene.)