I'm an old man, Jusum. I was a womping 24!
I'd have to agree with you and say the best production was easily Siamese Dream. The production value was almost "prog-rock" in a way. Reminded me of the kind of artistic approach to production I liked so much with Pink Floyd, early Genesis, and Yes.
And yea, in terms of guitar sound, Siamese Dream kind of ushered in a fascination with the "huge guitar" sound and chainsaw distorion ala the Big Muff Pie and Foxy Lady.
Vitalogy is by far the most under-rated album of that time. I think everyone was hoping for another hit machine like 10, but instead, they got these really thoughtful, deep, and interesting textures. I think it's their best work ever. When I first listened to it, I said: People aren't going to understand this just yet, but I'll bet in 10 years, we'll listen to it again and love it. I can just play that album over and over and I always hear new things in it that I like.
The guitar work was very "textural." I guess that's the best way to describe it. But very nice.
Sonic Youth - also very under-rated. The guitar work on No Star, like everything else, was more like a piece of abstract art. Not particularly musical, but it certainly made a statement.
Not since the Beatles have I heard an album like Purple. Don't get me wrong, here -- they are NOT in the same league, but I thought Purple was one of the few albums where every single song, if not already a radio hit, was at least "pretty good." There were absolutely NO songs on it that sucked. Certainly nothing new in terms of guitars, though. Very Jimmy Page-esque in a modern way.
The Division Bell was pretty weak for a Floyd Album, but it's always nice to hear vintage Gilmour guitar playing. I remember listening to the intro to "What do you want from me?" and feeling those guitars growl and resonate from my belly. Wow! And his work on "Keep Talking" gave me chills. Sadly, it's probably the last we'll hear from him.
As far as the 90's as a whole, I'd have to say OK Computer, followed by Blood Sugar Sex Magic, then Siamese Dream, then Ritual De Lo Habitual. And the order could change, depending on my mood.
These could all deserve a spot in the top-whatever best-produced albums of all-time.