I prefer the 1968 and newer ones. They had a 12V electrical system starting in 68. The older ones were good but with 12 volts you get brighter lights (and sealed beam headlights) and a stronger starter.
from a reliability stand point. there is no difference. the basic differences other than bigger engines throughout the years are minor. larger tail lights, different steering wheel irs suspension introduced in USA in 1968. pure die-hard vw enthusiasts will say the older the better, but in my opinion anything 1977 and older is awesome. i also dont really care for super beetles (i dont like the way the hood curls under the bumper and the curved windshield on 73' and later supers) i do like the smaller tail lights of the 1972 and earlier (the older the smaller and less complex the tail light design) 1973 was the first year for the "elephant foot" tail light, my 75' has them but they still look good when new and shiny. i also like the 'long' decklid of the earlier bugs, 1967 and earlier.
overall they are the same car just look slightly different. its up to your personal preference as to which year you really want. think of it this way....do you want something that a lot of vw collectors and purists will really love (1963 or earlier), or just something to tinker with and have fun restoring and/or driving(any year will be fine)