Of the 3 I listened to PJ the most, although lord knows Nirvana was permanently burned into my brain as much as I listened to it.
In no particular order, what they represented to me:
Nirvana - since I had just started playing guitar, Nirvana didn't do much for me upon first listen. Sure it was great that SLTS was easy to play, but the music was pretty boring. However, Nevermind was an album that drastically opened up the more I listened. It went from being noise to suddenly having melody. Once I heard the melody, the simplicity was amazing.
PJ - I remember buying 10 and SG's BadMotorFinger at the same time, a few days before seeing PJ open for SG at the Bronco Bowl. I was barely 16 and had zero business (nor balls) to drive from my small town into Dallas. My best friend's parents drove a few of us down, then picked us up afterwards. We were the first people in line that already had tickets. I remember standing outside and hearing PJ soundcheck to "Once". PJ was also a band that took a few listens for the hook to set, but once it did I was mesmerized. Like the progression of the intensity in each of their songs from the start of the song to the end, I almost felt like I began to vibrate as I lost myself in the music.
SP - I instantly loved them when I first heard Cherub Rock, then was ecstatic when I heard the rest of the album had the same hard rock, extremely melodic, and <gasp> guitar solos that weren't blues based noodling but sounded crafted for the song....Loved SP. Oddly, it was the album I listened to the least of these however. I don't own it today, but keep telling myself to add it to Spotify. I never bought another SP album, although there future radio hits were hummable.
I still listen to AIC and Soundgarden, going on a kick at least once a year. I still go to their concerts occasionally. I can't say the same for PJ, and SP is a moot point.