I have not been on Holland but I can tell you that Summitt is terrific. You willl not be disappointed. If eating is important, make sure you eat at the premium restaurant which is $20 or $25 addtional. It is a bargain at twice the price. When my wife I an go on "X", we scramble to get reservation as soon as we get on the ship. The food on Summitt is generally very good to excellent but the premium restaurant is like a *** Paris restaurant.
For tours, the best may be right on the ship as seeing the works of the P.C. is interesting. The only down side is the virtual lack of security you witnesss by the locals who "guard" the canal against terrorists.....'wink, wink'. On another trip to Panama we went to a villiage in the jungle to visit one of the primitive tribes. This was very good. Be prepared for very hot and wet weather.