I only like Guns N Roses up until Adler left. So I guess for that reason I’ll choose Zeppelin. Their music is so different though its not really a fair to pick between them. Axl is an asshole but I don’t like Robert Plant all that much either… Jimmy Page and Slash/Izzy are my favorites in both bands.
I also think its more respectable that Zeppelin never replaced any of its members, and decided to break up once Bonham died.. Where Guns N Roses is still a band today and the only original member is Axl. And they replaced Adler and Izzy so quickly without it even being a debate.