All but one evening of our stay in Budapest will be filled with concerts and opera.
Which would you prioritize for our open evening to see the lights of Parliament, etc.--one hour cruise or up Castle Hill?

Either would be lovely and doing both if the timing works would be a delight, but if I had to choose between the two, I'd go for Castle Hill. Many moons ago, I dined at a restaurant at the Fisherman's Bastion there. Watching the lights of the city blink on, reflected in the river, is one of my favorite memories of that trip. The restaurant at which I dined closed long ago, but there is a restaurant there now that gets decent reviews. It might be worth investigating.

Enjoy!

Can’t you do both? We did a 1hr cruise last year and seeing tge bridges and monuments, especially the Parliament, up close, was most special. We were done by 8.30 and then went on to a very nice dinner, though it was not on Castle Hill. But you could book a latish dinner after the cruise, so it is most doable.

I agree!