Not really. Illustrator is better for the drawing stage of your UI than Photoshop but both are equal when it comes to checking spacing, color values, corner ra

Not really. Illustrator is better for the drawing stage of your UI than Photoshop but both are equal when it comes to checking spacing, color values, corner radiuses and so on when it's time to actually build that UI. It's also a bit more straightforward to export an object drawn with Photoshop than it is to do the same with Illustrator. Also, decent-to-good "Photoshoppers" are a dime a dozen because both businesses and schools have a weird love affair with Photoshop but decent-to-good "Illustrators" are harder to find. You'll have a hard time convincing your client to make its team of ADs and designers switch to Illustrator.