Well, i meant both, although strongly the one what Spunky said.
1.5 was actually considered as the 'Last Real' Cs, since VALVe decided to make the mod as an trademark, to be sold as in Cs-Anthology, and in other packs, but before that, it was a mod.
1.5 and 1.6 are both good, but i still like 1.5 more for my own reasons.
1.6 didn't exactly ruin Cs, but there were some things that made it go down a bit. de_aztec for example, is a whole different map between 1.5 and 1.6 , and i liked the old one better.
Most important is in the end, that it's the same game, with same gameplay, except for some little things, and the community is pretty different when compared to each other.