I have bought the full pack of CS and i play CS:GO mostly on my imac. On my macbook pro i play CS:S i find CS:GO more competitive and more "real". Also, imho, it can compete with other modern fps like B3, MW3 etc...
I played 1.6, Source and GO and I like Go the most, but I'm like super casual in CS, a big noob and don't like CS in general. Still, GO is the one I disliked the least.
Different games. Older does not mean less good. Original Unreal Tournament is nearly 15 years old, people still play the newer "versions", despite mostly the same weapons, etc.