Depending on your style, but for me I would be leaning towards either the top time or the seamaster, with the santos close behind. I would go with whichever most fits your style, though. Are you more outdoorsy? Seamaster. Are you more classy? Santos. Do you have a more chilled out and laid back vibe and own a Shelby? Breitling. Do you cook meth? The Tag.
I would go with a citizen promaster dive watch. Solar powered, durable, low maintenance. If he isn’t super into watches, it’s perfect.