I had a list somewhere on here earlier.
Its not accurate anymore, so I'll be changing it.
Classic Series (Divided into two sections since I find the 8-bit games play differently from the other ones):
Favorite 8-Bit: MM3, did so much right and is a decent challenge even to this day.
Least Favorite: MM9, Capcom nostalgia wanking, going backwards on advancements in gameplay (Only keeping rush and the speedier ladder climbing from later games.)
Favorite Post 8-Bit: MM7, Wonderful music, fun weapons, great ending. Always a blast to play.
Least Favorite: MM&B, specifically the GBA version. Lame music, unrelenting difficulty, bullshit dash controls (SFC version didn't have this problem because of a dedicated dash button. [tornado fang] command dashing.), Bosses have far too much invulnerability time.
X:
Favorite: X2, perfect blend of good levels, freedom to play the game with as many or as few upgrades as you want. Truly the best 16-bit X in many cases.
Least Favorite: X4, dull music, probably the worst X armor (Weak hover that only works for a few seconds, [parasitic bomb] buster, Helmet was the only good thing about it.) X doesn't have much in the way of story or significance to the story, probably only there because it wouldn't be an X game without X.
Zero:
Favorite: Z4, Ended the story in style, kept most of the enjoyable extended cast around, added a few more, good boss battles. Rankings optional finally.
Least: Z1, this doesn't mean its a bad game, it did a lot of things really well and did some original stuff like an almost completely connected world. But the ability to fail a mission and lose access to it entirely is a downside, and leveling weapons up to use their charge attacks or complete combos is not fun in the least.
Battle Network:
Favorite: BN6, probably one of the best Navi customizers, decent story, great chip selection, cross system is good.
Least Favorite: Tie between BN5 and BN4, Mediocre Navi Customizers (In BN4's case awful since its the one with the least freedoms, thanks to no Compress codes.), Story in BN4 is almost nonexistant thanks to the game being almost entirely tournaments. BN5 has painfully dull Liberation missions, story is okay. Dark Chips in both games are essentially worthless save for in BN5 for chaos crosses. Soul system is a lousy replacement for the Style Changes of BN2 and 3.
Starforce, ZX, and Legends all get excluded from this as ZX only has two games and I never played the entirety of Starforce or Legends.