Personally my favorite Megaman titles are 3, 7, 8, X2, and X4. They are fun, easy for casual players to grasp in my opinion. And 3 has great music!
As a side note, you could try Megaman Zero if you can get your hands on it. That one was super fun even though I don't remember any of it! I think that one was easier than the NES Megaman games.
If we are talking about hacks though, try Rockman 4 Minus Infinity. It is definitely one of the best hacks out there, of all hacks ever... or maybe just for Megaman hacks in general. Not so "easy", as it does bring it's own challenges, but it's a must if you are into the Megaman games and want something better than any official Megaman title. *gasp* yeah I said it.
As a side note, you could try Megaman Zero if you can get your hands on it. That one was super fun even though I don't remember any of it! I think that one was easier than the NES Megaman games.
If we are talking about hacks though, try Rockman 4 Minus Infinity. It is definitely one of the best hacks out there, of all hacks ever... or maybe just for Megaman hacks in general. Not so "easy", as it does bring it's own challenges, but it's a must if you are into the Megaman games and want something better than any official Megaman title. *gasp* yeah I said it.