Jesus, Nirvana was so much better than Pearl Jam. Fuck, I think Pearl Jam's Ten was MUCH more poppy than Nirvana's library.
Seriously, Nevermind was like their only really "mainstream" sounding album, and that's because it basically was produced to perfection. They couldn't replicate those performances live.
If you want to see where Nirvana was heading before Cobain, listen to In Utero and listen to Unplugged in New York. That may be the easiest conclusions to make, but it seemed like Nirvana was really going towards plugging in a few songs that sounded like Bleach on steroids (Scentless Apprentice, tourette's) with songs that sounded like they were made for the acoustic set (Pennyroyal Tea, Dumb)
One of these two sounds would have won out, and I would think the latter would have (MTV Unplugged in New York), although You Know You're Right would be a good argument against that. I could see new wave coming from Cobain, but crazy, off the wall shit was just as likely.