Windows 8 - I didn't like it at first but love the speed, reliability and great memory management. I think this is the first windows which i am hapy to just leave on without reboot every day or so to get the memory back in order.
Windows 2000 - Incredible release, i was a big fan of the NT range and this fixed a lot of problems with NT. Fast, lean and very stable.
Windows 95 - Loved it at release, great new UI at the time and finally a version of Windows to get me away from DOS. i would say OSR2 was my frav as it brought FAT32 and better USB. Still can remember the feeling of loading up 2 full music videos from the CDROM Weezer's buddly holly and the other one, full screen it was amazing!!
Windows NT 4.0 - Incredible OS. ultra lean and very quick, very stable i loved it. I used to dual boot between Windows 95 and Windows NT 4.0.
Windows ME - Fastest version of Windows for games. When compared to Win95/98 and XP Windows ME consistently provided higher framerates, it was really good at games.
Windows 7, great rewrite from Microsoft, what Vista should have been. started the incredible trend of Windows needing less resources than it previous versions. Loved the new task bar and performance..
Clients i hated
Windows 3.0/3.1 and 3.11 - Slower and not really of any use. I only used these when i had to use office. Extra memory would mess up and slow up DOS games, windows games were non-existent apart from solitare and the mine thing. It was alright for work, but was unstable and just horrible. Windows 3.11 went some way to fix some of the networking issues, NT 3.51 solved some of these however at the time Novell Netware wiped the floor with it in a network.
Windows XP, taking the great performance of Windows 2000 and slapping on a childish UI and other junk which slowed it down. I hated XP, only used it when i had to, the only version of XP i didn't mind was XP x64 and that was because it was mainly Win2k3 SP1 and performed quite well. XP was a massive pain for me as XP really come into it's stride during the virus years so i was constantly maintaining antivirus software and cleaning viruses, bloody thing was like a virus magnet. SP2 helped a bit, but it took years to get the virus situation under control.
Windows 98 for the same reasons as XP, it took the lean and fast Windows 95 and stuck on a crappy UI with the extra crapola IE4 active desktop component, what a great way to throw very expensive memory down the drain, that and those horrible themes, it makes me wince now. People getting PC's with 8MB RAM and loading every theme and having that crap active desktop, the PC used to simply struggle doing that let alone any work or playing games.
Vista - Hated it, used it in Beta and on release multiple times. Resource requirements where high at the time, problems when copying files from/to usb. Copying over a network would crawl if playing a video. Crashes with video drivers, most other drivers not working. Memory usage bugs such as SVCHOST and others. Problems going to sleep, problems coming out of sleep. Problems with wifi, especially when going in and out of sleep. Vista was beta till SP1. (PS problems described were not on a single PC but on a range of desktops and laptops).
Windows 2012 - near perfect, give me checksum in storage spaces with multiple file copies across the array a la ZFS to prevent bit rot and it would be perfect. Performance is great, love being able to cut down the UI, love de-dup, works exactly as described, uses hardly any resources especially when compared to ZFS. Stable and just generally great!
Windows 2008R2 - great version, first proper version of Hyper-V from the buggy Win2008 version
Windows 2003 - Very fast, great performance, very stable.
Windows 2000 - remember the big switch from domains to active directory. The fun getting to grips with DNS on a local network. It was great though, finally got the novell features that they used to brag about, a full on directory based system. Stable system too
Windows NT 4.0 Server - loved it, used to love deploying this, this an exchange or SQL Server was so much fun. Easy and would just work. The kind of server you setup and forget as patches were generally only applied when there was a direct problem with the server as most of these were offline anyway. The amount of times one of these would be setup and forgotten about as they just ran without any problems. I haven't done it yet but i want to test out NT 4.0 as i think NT 4.0 actually has better thousands of small files file sharing performance than even Windows 2012. I remember when switching some users from Windows NT 4.0 to Windows 2000 and it causing a problem as some applications such as Sage Line would be comprised of 1000's of small files and Windows 2000 couldn't match the file sharing performance.
Servers i hated,
None they were all great, i didn't mention Win2008 as i didn't really bother with this version and jumped pretty much from 2003 to win2k8r2