Wow.... so difficult!
Every release, especially OS X Server 1.x (not in this list), gives me sweet memories.
Mac OS X Server 1.x:
The first taste of the move from NeXTSTEP to Mac OS X. Aka "Rhapsody", this OS was something really different for us Mac users! It had the Mac OS 8 - styled "Platinum" look, but this OS could not be more different from Mac OS 8. This version was basically NeXTSTEP, and the setup and usage was more akin NeXTSTEP than Mac OS 8. But it gave the user the idea which way Apple was heading: a UNIX OS with an Apple-styled GUI.
Of course, the GUI changed dramatically over the Mac OS X "Client" development period, changing from "Platinum" to "Aqua" between DP 2 and DP 3, and the adding of the Carbon API.
Cheetah:
When OS X 10.0 came out times were exciting for being a Mac-enthusiast. Still on just a 500 MHz G4 (the fastest Mac at the time, while Intel was @ > 1 GHz...) , exploring the new Apple-NeXT OS. i.e. Mac OS X, was fun.
Bad times to try to support Apple (Mac OS 9 was pretty soon dead, the G4 was damned slow, and OS X was far from polished), but cool to play around with.
Puma:
An update to OS X which made it "useable" for the not-so-demanding user. 10.1 was faster than 10.0, but still, well.. eh...slow. Office v. X came out, so one could actually do some work.
Jaguar:
The first update that pushed Mac OS X really forward. Much faster than 10.1 and more apps were native running (Carbon or Cocoa). Also, the CD's of Jaguar were the most beautiful printed OS CD's ever. Mac OS 9 is now losing ground.
Panther:
Yep. Mac OS X 10.3 was the first Mac OS X release that actually made using Mac OS X far, far better than Mac OS 9. Fast, stable, looked great, good support, all the needed apps, etc. Along with the beautiful iMac G4, the Mac was back where it belonged: simply great.
Tiger:
Fully stable, looked good and Spotlight. Every Mac user was now onto Mac OS X. even the die-hard Mac OS 9 fans had upgraded by now...
With 10.4 came the first Intel version of Mac OS X. Times were going to change....
Leopard:
How cool to use a both PPC and x86 "universal binary" OS..? Leopard gave us a new look and the compatibility with the Intel world. Eithe ron a Quad G5 or MacBook Pro, 10.5 ran superbly.
But... this OS was the last Apple OS to run on PowerPC Macs.... From System 7.1.2 to Mac OS X 10.5.8, the PowerPC gave Apple a bumpy ride: ups and downs....
Oh well, just my $ 0.02