It's probably not as bad of a question as many think it is. The only real difference is Mazi has struggled for two NFL seasons, Guyton has struggled for just one NFL season.
Guyton
23 years old (June birthday)
668 NFL snaps
1,092 college snaps
Mazi
23 years old (June birthday)
828 NFL snaps
1,227 college snaps
Overall I'm not very high on either player, but both should probably be viewed similarly in terms of development time. Mazi technically has more time in the league, but overall has seen the field just slightly more than Guyton has. Both drafted as high physical traits guys that needed development.
Gun to my head I would take Guyton, but I'd rather have a 3rd option