The age-old 'castle side trip' question

I can see the dilemma but I would not dismiss Konopiste so early. It has the history and so long as you avoid (or not spend too much time in) what they call the "hunting corridor" then you'll avoid most of the taxidermy. There are also lovely gardens and it's a 30 minute trip from Prague which makes it a half-day tour. If you are restricting yourself to the other two then a note about Krivoklat. It is less touristy but the drawback there is that there are few organised tours that go there and if they do it's normally combined with something else like a glass factory etc. If you just turn up to the castle you'll find many internal parts are not accessible unless you do one of their castle tours and they don't offer much in the way of English options because....it's not touristy.

Karlštejn is probably the classic castle day trip from Prague, but I
get the impression the immediate surroundings having become a bit of
kitschy tourist trap as of late. Also, the interior is apparently
nothing special according to Rick.

I visited some years back and enjoyed it. The coutnryside was pretty nice on the way down and in the immediate area. But now that I know Rick says not to go .................................

As for the intereior, this is basically a 16th century castle so for the most part its going to be without a lot of ornamentation with a few stunning exceptions like: https://www.hrad-karlstejn.cz/pamatky/karlstejn/fotogalerie/interiery/2-okruh/p2260027.jpg .

@Jason - That was part of the appeal of Křivoklát to me. I usually do not hire guides in such places anyway (if I'm given the option). So, taking the train myself, joining a Czech tour and following along on my own in a book or from an English translation of the tour would suit me just fine. Also might be a good opportunity for me to practice pronouncing that elusive Czech Ř!

Good to know about Konopiště that the taxidermy is easier to avoid than I had thought. I had been a bit dismissive of it originally but if I don't end up doing Křivoklát, then I may reconsider Konopiště over Karlštejn.

We visited Křivoklát and Konopiště, We had our best tour of a castle while at Konopiště--it is definitely more than just the stuffed animal heads. They also do NOT allow photos to be taken inside, which to us is a big plus. People trying to get the "perfect" shot to put on social media is off-putting to us while touring castles.

Křivoklát - you will most definitely not run into crowds here. Yes, there is an English translation booklet you can purchase here for the tour, but there was obviously more info given to the Czech speakers that was not in the booklet. This visit won't take you long. If you have a car, a visit to Rückl Glassworks in Nizbor is close by. They give fascinating tours of how they make the crystal. In their showroom you can typically purchase crystal for less than in Prague.