Happy New Year + Happy Cruising
Mostly I am checking the price of the shore excursion. If I can get for the same price a local tour operator with personal car and guide for same or less, I book them because I can point out what I am interested more or less.
The other advantage: you do not follow the group (especially if you have lot of elderly guests) from one toilet to the next.
Just google and you'll find them.
Should you stay in the city of call or go to an inland destination: hard to say:
e. g. Zeebrugge:
If you never been in Belgium before I would go to Brugge (next town) or Brussels. If you have been there you can also go to places like Waterloo (Napoleons battlefield) , Antwerp (to buy diamonds...) or Ostend (seaside).
I can also speak for Amsterdam: the cruise terminal is just at the backside of the central railways station. Just pass it. In the front you will find the tourist office and some operators offering the canal (GRACHTEN) trips which is much more cheaper than on the boat. In Amsterdam you can go to see Rembrandt's Museum and you can get it by bike or just by tram. If you have been already in Amsterdam you can also go to places like Keukenhof (Tulippark) or Gouda, Edam, Alkmaar (Cheese-markets) or of corse Delft (the Dutch China town).
You see: a question of budget, willingness to check your self and personal interest. No general recipe.