we will be staying in Prague and visiting Cesky Krumlov. Wondering if just walking the grounds and gardens in Prague and touring the castle in Cesky Krumlov would be the most interesting.
In Prague, I found the castle Cathedral to be well worth the visit, including the paid-entry ticket that allows you to make a circuit inside. (Otherwise you can admire from inside the front entrance for free.) You might look into the Rick Steves tip for getting to the cathedral just at opening time to have a few moments of relative peace before the tour groups arrive.
In Cesky Krumlov, I really enjoyed the tour of the Baroque Theater, though I did not tour the castle.
Cesky Krumlov castle
Note that it is closed Nov-March, as is the theater mentioned.
Just note that at Prague Castle the South Gardens (scenic city views) are currently closed. The Imperial Gardens are open until November 30th. Garden on the Bastions is accessible all year.
Golden Lane is wonderful to tour; it’s within the Castle complex. Golden Lane has the cottages where the workers from a few hundred years ago lived and worked. Fascinating. You are peeking into the past and many of the cottages have been turned into quaint shops where you can buy souvenirs. It is not kitschy or touristy. It is interesting and worth seeing.
The two sights are not similar. The CK castle is much more of a very old residential chateau, not a stone castle. Are you making CK as a daytrip or spending the night? CK is a very long distance from Prague, so your free time and scheduling tour-only interior visit tickets can be important. Strolling the town exteriors of CK is very enjoyable.