Having finished my rewatch of most of* the MCU, my ranking:
*I skipped Incredible Hulk for irrelevance to the subsequent MCU, and Ant-Man for apparent irrelevance to Infinity War in particular; I'll rewatch the latter closer to the sequel anyway
Phase 1
Captain America: TFA
Avengers
Thor
Iron Man
Iron Man 2
Phase 2
Captain America: TWS
Iron Man 3
GotG
Avengers: AoU
Thor: TDW
Phase 3
Black Panther
Thor: Ragnarok
Civil War
GotG2
Spider-Man: Homecoming
Doctor Strange
Overall Best: Tie between TWS and Black Panther, though this could change on another viewing of the latter; Runner-Up: Thor: Ragnarok
Overall Worst: Iron Man 2; Runner-Up: Thor: TDW (undoubtedly the most formulaic and rote sequel the MCU has produced to date, but it still maintains a certain basic level of filmmaking and screenwriting competence that IM2 can't)
Most Underrated: Iron Man 3; Runner-Up: Thor 1 (it feels awfully small given the premise and budget, but does a much better job establishing Asgard and its relationship with Earth than it's generally given credit for)
Most Overrated: Iron Man 1, with no real runner-up; RDJ's performance just doesn't seem as fresh after he's reprised the role so many times, and the post-9/11 military worship and fixation on vaguely Islamic terrorists haven't aged well
Phase 3 has definitely been the most consistently high in quality overall; its weakest film to date, Doctor Strange, is still much, much better than the worst of Phases 1 and 2. I'm sure the 2015 Feige/Perlmutter split isn't the only reason for this, but it can't have hurt.