Deulofeu plays in a front two at Udinese, not midfield like Guendouzi. And is also a winger like Danjuma, so would presumably take Bailey's position in the team. He is also not 31, he's 28.
According to Transfermarkt Deulofeu has missed 61 games through injury, whereas Danjuma has missed 86 despite being 3 years younger.
Danjuma has had ONE good season with Villarreal and having CL experience is irrelevant (See Sanson, Digne, Coutinho).
Danjuma would also likely cost 2 possibly 3 times as much as Deulofeu, and with no guarantee he's going to be that much better.
Ultimately it will be whoever Emery believes is a better fit for the team.