We are going to Sicily in May, 2022 and want to add on Naples at the end. wondering which ferry service is the best for overnight accommodations. There's one that has two berths in private room. that looks to be the best, but just wondering from all you experienced Sicily travelers out there. Thanks in advance!!

We loved our time in Sicily and Naples three years ago.

I am sorry I don't know about ferries. However, I know you didn't ask, but we took a flight from Naples to Palermo which took about an hour. I think the price was quite reasonable.

There isn't a big difference between Tirrenia and GNV. Both companies offer 2 berth cabins, restaurants, bars, etc.
As the journey lasts 11 hrs only, you will spend may be 1 hr in the restaurant and most of he remaining time in your cabin anyway.
The size of the boats is similar.

Thanks so much for letting me know. I couldn't find the two berth cabins on one of the lines. But we were able to find one and book it! Glad to know both options are good.