1.6.4 Forever.
I believe 1.7.10 was the last version of pre-Microsoft Minecraft but 1.6 was great too.
1.7 fucked a lot of shit up in regards to biomes.
So what that we have to run cracked launchers to play the ancient craftbukkit server. Fuck microsoft, I closed my account when they started wanting everyone to go to a fuckbox login. Fortunately I still had all my payment info.