Ferry from Dublin to Holyhead

I took Irish Ferries. I didn't realize Stena was an option.

There is a large seating area with snack bar on Irish Ferries. I'm not sure why you would need more for the relatively short crossing?

I guess the advantage of upgrading to Lounge seating would improve your changes of (a) slightly larger, more comfortable seats and (b) avoiding rowdy folks in the equivalent of steerage. On most ferries the latter isn't an issue, but I remember a Scandinavian crossing on a Friday night that got pretty noisy and unpleasant with passengers trying to get their money's worth at the onboard bar, as liquor on the boat (I was told later) was cheaper than in the destination country.