Me personally, having been an AC/DC fan since i was old enough to know who they were, I prefer Bon Scott. Brian is a great singer and took the band to a different level, but Bon's crazy, silly, wacky attitude really complimented what the band was at the time. A wild n crazy, not to be taken too seriously,Rock N Roll. Listen to songs like "Soul Stripper, Night Prowler, The Jack, Sin City, Jail Break, Whole Lotta Rosie, and stuff and you'll see what I mean. These are the AC/DC songs I really love.
With Brian, the band became more serious, more "poser" I guess. It seemed to me more like that dude you knew in highschool that was a nice guy, got good grades and had rich parents, but tried to be a bada**, wear raggy levi's and an AC/DC T-shirt while being captain of the chess club and driving that new beamer his parents got him for his 16th Bday. It almost seems like Brian was trying too hard to fill Bon's shoes or prove himself rather than having the AC/DC attitude and saying, "Screw it. Im gonna do whatever pops in my head at that second."
Just my opinion, and maybe Ill get some crap for it, but in traditional AC/DC fashon.."screw it" lol. ;)