We had a cruise stop in Le Havre a few years back, and we've been to Paris several times. We opted for the excursion to Rouen because we hadn't been there but wanted to see it. Rouen has a beautiful center, with a famous cathedral painted multiple times by Monet, an interesting "plague cemetery," half-timbered medieval streets, and the place where Joan of Arc was burned. There's also an art museum with a good reputation which we didn't have time to visit.
I wouldn't recommend the Paris excursion because most of it will be going to and from on a bus. I'm sure there's some nice scenery on the way but also a lot of unattractive suburbs and expressways. A few hours in Paris won't go very far, and you may spend much of that time on the bus looking at things from the street. Paris is a fantastic place to visit, but I would give it at least a week if possible. You might think that a vey short visit would tell you whether you like Paris enough to return, but the risk is that the rushed coach experience might skew your perception to the negative. Take the city on its own terms with a longer visit. I could spend a month there easily, others maybe not, but just a few hours isn't worth it.
I haven't been closer to LeHavre than the dock area, but it was heavily bombed in WWII and not much is left of the old city. There is a very good art museum, and a remarkable bridge across the Seine that you might see from the highway on a Rouen or Paris trip. You could probably get into LeHavre easily enough by taxi.
Another option, which you didn't mention, might be an excursion to Honfleur and/or the D-Day beaches. That might also be a worthwhile choice. Honfleur is so close to LeHavre that your bus time would be minimized.