Think i might also give a tie between Mega Man 2 and 3 instead. I had to think about what i hated more, the turret boss in Mega Man 2, or the Doc Robot stages in Mega Man 3 and i hated the Doc stages more.

Mega Man 2 is my favourite.

Voted 7 as my favorite because i love the visuals, music and bosses. Did ya'll know there's a NES version for PC?
http://www7.atwiki.jp/wakuwakusuru/pub/final2.zip

but in terms of best overall in quality i would vote 3.

3, easily. For the music alone. It was also the first game in the series I played. And Spark Man was the first level.

For me, from favorite to least fav:

Mega Man 9
Mega Man
Mega Man 2
Mega Man 10
Mega Man 7
Mega Man 6
Mega Man 5
Mega Man 4
Mega Man 8
Mega Man 3

Imo, there is no 7-10. Megaman 1-6 on NES was it. I would put Megaman 2 first with the 3rd close behind. The first one is the hardest though and the one most people should be proud of beating (assuming they're playing the real game on a real console. Using emulators and cheating via save states is just that, cheating.

1. Mega Man 2
2. Mega Man 3
3. Mega Man
4. Mega Man 9
5. Mega Man 4
6. Mega Man 10
7. Mega Man 5
8. Mega Man 6
9. Mega Man 7
10. Mega Man 8

I'd really have to replay them all in order to list them accurately, but MM2 is definitely my favorite with MM3 next.

Megaman 3, then 2 and then 1. then 6. haven't played the others to compare with.

I'll be honest, I've never played a single Megaman game. It's a bit shameful since I had all Nintendo consoles and I've never bought a single one! XD. I definitely have to try them, but they seem... really hard.