Cinque Terra Or Ravenna ?

I think the bigger question is what you're more interested in doing/seeing? Comparing one to the other is comparing apples to avocados: they're very different places. The CT - which will likely be very busy in May - is better for people who enjoy hiking and other outdoor activities.

Ravenna's stars are its eight UNESCO World Heritage-designated, 6th-century Byzantine mosaics, and its architecture; as a 5th century capitol of the Western Roman Empire, it's a draw for history, art and architecture lovers. As it has become a port for large cruise ships over the past couple of years, it could also be quite busy but I've not heard how that port change has affected crowd levels.

Also, where would you be going after these 2-3 days?

What are you interested in and will you have a car? Last fall we did a driving trip from Volterra north along the coast of Tuscany and then west along the coast of Liguria almost all the way to France, however, skipping the Cinque Terre and actually almost all of the coastal towns. Our main interest was food and Etruscan art and early Renaissance art, not scenery, hiking, or beaches. The Cinque Terre is too crowded for us.

You could get to Ravenna in about three hours by car or train, if you want to see the mosaics there. I would think you would need to spend two or three nights in Ravenna just to see most or all of them, but if you had a car like we did there are some interesting nearby coastal towns like Cesenatico with its open air ship museum. Or Comacchio (a bit inland) with its triple bridge and canals and eel cookies (they just look like eels).

Kathy ALWAYS types faster than I do!

LOL, Nancy! I'm actually a TERRIBLE 2-finger typist!
No matter; Minnesota Minds are on the same page regarding CT versus Ravenna! :O)

I spent 3 nights (just 2 full days) in Ravenna during mid-September 2022. I was very pleased to find the city not swamped by cruise-ship hordes; I may have been lucky in my timing. The main square was lively, and the streets weren't deserted, but I didn't hear a lot of English. It was great. I really like Ravenna; this was my second trip there. In addition to the key mosaic sights, there are several worthwhile museums (including a new one out in Classe), and the historical center is quite attractive. I rushed and just about finished my long list of sightseeing targets in two days; I got to the church (St. Apollinare) in Classe but not to the new museum. I still haven't been to other towns in that area.

In May 2019, I spent a few days in the Cinque Terre (not my first visit - I love it), then trained east to Ravenna for a few nights before heading to Venice.

It was my first trip to Ravenna. It was a nice town, but it didn't blow me away or anything. The old mosaics were pretty cool but not really my thing. I took a day trip out to Rimini, which was a pleasant town. I walked out to the beach, which is pretty boring compared to the Cinque Terre. Perhaps the coast is more scenic elsewhere.

The Cinque Terre gets very crowded as you've no doubt heard. There are ways to avoid the crowds. Also, you can expand your horizons to the rest of the Italian Riviera e.g. to the north near Portofino: Camogli, Rapallo, and Santa Margherita Ligure are all really nice towns, all far less crowded than the Cinque Terre. There are hiking opportunities in this region as well, even if the scenery isn't quite a good as in the Cinque Terre. (I spent a few nights in Camogli a few years earlier and it's a sweet little town. Google for info/pictures of it.)

acraven: How amusing. We too were in Ravenna for 2 nights in Sept 2022 - 17-18. We might have passed on the street.

As we have read many books about the early church and Italian history, we were very happy with our stay. We had no problem seeing all but one site (the church out of town) in 1.5 days.

No contest, Cinque Terre. I recommend starting early as soon as sun rises, then heading back to whichever of the 5 towns you are staying in for a break, then heading back out. I felt the crowds peaked 11am-4pm when I went in April. I also recommend the local train pass for 3 days, it includes WC.

Personal preference - Ravenna. Then the beaches at Rimini and perhaps a side trip to San Marino.

For Ravenna, if you have any flexibility in your dates/itinerary, you can check cruisemapper.com. From there you can see which ships will be in port (called Porto Corsini), how many hours they will be in port and each ship's number of passengers and work around that.
There are other websites as well.

I'd look at the travel time while considering what your interest are. Are you driving at all on the trip? You would likely not need three days in Ravenna but if you have a car, you could do some nature activities (which is the only reason to go to crowded CT (IMO, obvs)--to access great hiking without a car).