TPM was the first one I saw. I went to the theatre with my Mum as a little kid and watched it, then rented it quite a few times after that - and eventually bought the VHS. The action was great, I had no idea what character development was, and the CGI looked real to me (imo the CGI in TPM is better than in AoTC/RoTS). Then I saw Toy Story 2. Irrelevant, right? Well, no. You see, in Toy Story 2, it turns out that the evil Emperor Zurg is Buzz Lightyear's father. As I was watching Toy Story 2, my Dad turned to me and said "You know where that's from!" and I was like, "What?" and then he was all "Star Wars! Darth Vader is Luke's father!"
That's right. My Dad ruined the Original Trilogy for me. I hadn't seen Empire Strikes Back before then, and I never got to experience it in the way that so many others did.
I didn't realise the significance of that at the time, though. I borrowed Empire Strikes Back and Return of the Jedi on VHS (the pre-1997 versions, no less) and watched them religiously, until I was given the Special Edition boxset that Christmas. I was still in awe of it all; the Jabba scene astounded me ("How did they make a CGI character in 1977?! Wow!") and I would watch all of the films frequently - even though I thought of ESB as 'the most boringest' one.
Attack of the Clones rolled around, which I went to see a couple of times in the cinema. I didn't buy the VHS, as I kind of hated the love story - at the time I thought I was just plain immature but looking back on it now I realise that I never had a problem with the love story in ESB; the one in AoTC simply suffered from terrible execution. This was at the time and still is my most loathed film in the PT. The CGI was crappy, Anakin was a whiny teenager and I had no idea who Dooku or Sifo Dyas were.
Revenge of the Sith, I liked. I went to see it on opening night and grabbed a pizza beforehand. There were stormtroopers posing in the lobby, and the movie was simply a thrill - from the space battle at the beginning to the first appearance of the Emperor through to the image of the Death Star at the end. I was so caught up in the angst and special effects as a young teenager that I ranked this film above the Original Trilogy - something which I feel deeply ashamed of now.
It wasn't until I saw the RedLetterMedia reviews that I realised what a fucking mess the Star Wars prequels are. Not just the nitpicking, but watching clips from the films again demonstrated to me not only the awful CGI but the even more awful acting and scripting. I am now a total purist, and I don't really consider the prequels to be canon - the only information that I accept regarding the Old Republic era are snippets from pre-1997 video games and novels. They, in my opinion, captured the essence of the very brief allusions made by Kenobi in SW and RoTJ.