Guns n' Roses has a stronger body of work overall, but "Appetite For Destruction" alone propels them light years beyond Mötley Crüe. "Appetite For Destruction" is easily the strongest debut record in hard rock history. Each and every track is a classic. Subsequent releases failed to live up to it, but there are still some solid tracks on the "Use Your Illusion" records as well.
Mötley Crüe was a better band than a lot of the hair metal and glam metal bands that were sprouting up at the time. Their songs had more energy, more attitude and more substance to them, but musically, they were never at a level where they could compete with Guns n' Roses, especially in their heyday. Nikki Sixx has always been the most prolific songwriter for Mötley Crüe, and while he's always been a capable songwriter, his guitarist, Mick Mars, has always been a minamalist. He rarely went in for guitar solos and Mötley Crüe songs were much more straightforward and no frills compared to Guns n' Roses. To compare Mick Mars to Slash is to compare a toddler's finger-painting on the refrigerator to the ceiling of the Sistine Chapel. There is no contest.
To be fair, I think that Mötley Crüe has been more consistent, but to me, their early stuff was as good as it got. The EP and their first album were the best, and then they had a few good moments here and there on later releases, but essentially all of their good songs could be compiled on one full length album whereas with Guns n' Roses, they may never have hit the same heights they did with their first album, but that's the kind of record that a band builds a legacy upon. Imagine if that had been their ONLY album. They'd be rock gods. And it's not as though they weren't once, it's just that the aura faded with all of the petty infighting and the sub-par quality of what they went on to offer up later.
If the choice was "Both bands have just released a 'Best Of' CD, which one would you rather buy if you had to pick one?", then the answer would be Guns n' Roses. And if the question were "You can go back to 1988 and see one of them live, which one do you want to see?" the answer would be Guns n' Roses. One thing that I never got about Mötley Crüe is how weak they were live. They were never able to recreate their songs on the stage anywhere near as well as Guns n' Roses.
I go with Guns n' Roses any day of the week and twice on Sunday.