Well, from what i read from first post, i'll have only to say:

To be honest, here's what i think:
DM2
+ =Good combos, nostalgia cards, Fan Service
-= The Mainstream of constant winning and never losing (except few times), Games can be shallow sometimes.
GX
+= Perspective of School academy, Fan Service, good duels, and this is where i started to like Demise.
-= The Mainstream of constant winning and never losing (except few times), too much Fusion for me.
5'Ds
+=Synchros, Duel Runner, Fan Service, epic duels, Dark Story, dueling combos got more expanded.
-=The Mainstream of constant winning and never losing (except few times), it ended too soon.
Zexal
+= Xyz Monsters, some good characters, Dueling Combos got more expanded, Main hero loses once in a while.
-= Yuma and Kotori, too much warriors.
Arc-V
+=Spot the light on other summoning methods (Although, Ritual Monsters stayed in the shades of Dark 😞 ), focusing on different characters, not so much mainstream duels, i like the story.
-= Too much colors and rainbows, too much dragons for me, No Fan Service 😞