My favorite iterations of early Aqua are those seen in 10.2 through 10.4, too. 10.4 would be on top, but I prefer the matte menubar used in 10.2 and 10.3.

10.5 and 10.6's Aqua aren't bad and certainly better than the newer flat looks, but I was never a big fan of the darker metal look taken on by window chrome in those versions. Aqua in 10.2-10.4 was much more bright and cheery, and as strange as it may sound that reflected in my mood when using my Macs.

Out of the later iterations of Aqua I think the best is that of 10.9. It pulls back on the darkening brought by 10.5/10.6 while refining the rough edges that came with 10.7 and 10.8, and as a whole reminds me a lot of 10.2-10.4 Aqua minus the brushed metal.