I played 2-3, 5, 7-8. I gotta say its between 3 and 5 for me. I remember 3 only so much though and 5 is clear as day so I gotta go with 5

It's been fa too long since I truely played the series so it's impossible to give an objective answer, but probably one of the N64 ones.

I'm voting for it just because of that!

Mario Party 2 has the best minigames and some good boards, so I'll go with that one.

Mario Party 10, the bowser mode is criminally underrated.

Bowser mode is so much fun! Also, 10 has the best mini games I think. With classic mode it would have been the best by far (although it is still one of the better games). I think 6 is probably my favorite.

8 is by far the worst. Not only does it look worse graphically than 6 and 7, but a lot of the minigames are  just really really bad. A shame because  I think the boards are pretty cool.

Mario Party 3
Mario Party
Mario Party 5
Mario Party 4
Mario Party 8
Mario Party 7

The ones I played.

I played the first, 2, 5, 8 and DS, though I didn't own 2 myself. Of those I'd say 5 entertained me the most, though the first game's single-player 'mini-game island' or whatever was great. I heard most positive things about 3, so I guess objectively that one's the best. Too bad it's also the rarest one.

Mario Party 3 broke the mold with the battle royale boards.