I'd say it all depends on the situation, my friend. If you're out fishing during the day with your closest friends, you've gotta have beer. On the other hand, if the boat is in the slip and you're done for the day, it's time to get classy and mix some drinks.
The only time I've ever had anything but beer out on a boat was the times I've gone on bay cruises with a date. Sometimes they'll serve wine or even cocktails. When I'm alone or with buddies, I crack a cold beer every time.
I'm more of a sipper than I am a drinker. I can nurse a drink all night long and still have half of it left. On a hot summer day out on the water, I can drink an entire beer. So I guess "beer's" my answer.
Out on the water watching the sunset I like a long cocktail, maybe a gin and tonic or a wine cooler. Although I can appreciate that beer is good for most people I just can't drink that much liquid!
I don't drink alcohol, never have liked the taste much. Of course that makes me a popular guy as I get to chauffeur everyone else. Having friends who like to indulge, I have learned how to make a good cocktail. Making them on a boat can be tricky, but there's the beauty of modding, right?