We are going to be spending 2 nights in Lucerne, Switzerland in early May and I don't know which of the above we should go to - as we only have time for one of them. What do you recommend - and what are the pros and cons? And does it matter that we will be there the first week of May?
I only did Mt. Pilatus so I can’t compare the two. I can say I had an absolutely lovely day using the “gold ticket” approach. It covered all transport as I took a bus then the gondola up, the cogwheel train down, and then a lake steamer back to Luzern. Plenty to do at stops along the way.
The Mt. Pilatus cogwheel train reopens on May 18 only.
I've only been to Mt. Pilatus so can't comment on Mt. Titlis. I did the same as a previous post mentioned with the Golden Pass..... boat from Lucerne to Alpnachstad and then the cogwheel Funicular to Pilatus, returning to Lucerne using the aerial cableway down to Kriens. It was a very nice trip!
As a previous post mentioned, the cogwheel Funicular doesn't open until 18 May. However you could travel to Pilatus and back using the aerial cableway as that appears to be open. Here's the schedule - https://www.pilatus.ch/en/inform/timetable . The cableway is actually in two segments. A smaller telecabine (four passenger?) takes passengers from the bottom to a mid-way point and then the larger cars take passengers right to the top. As I recall, there's a short walk from the bus station in Kriens up to the cable car station (it only takes a few minutes).
In early May there should still be a lot of snow at the top of Titlis. Depending on your desires, it can be a good thing or a bad thing!