I would recommend taking the Swiss Trains while in Switzerland because they are amazing, and the destinations you listed are all easily accessible by train. In fact Zermatt is ONLY accessible by train.
Since you say you are going to Interlaken I assume you are going there to see the mountain villages like Lauterbrunnen, Wengen, Muerren and the Jungfrau. Of these places, Lauterbrunnen is the only one accessible by car, the other places are easily accessible by trains, gondolas, cogwheels, etc. In Interlaken you will see Lake Brienz and Lake Thun both of which are beautiful and a boat ride is quite exciting. You know, a Swiss Pass covers all of these journeys including the boat rides on the lakes. If you haven't already considered trains, then I would highly recommend you evaulate it closely. Training gives everyone the chance to see the spectacular vistas in Switzerland...even the driver :-)