The eastern Caribbean itinerary is generally good for people who like to shop, who like a lively atmosphere when they walk around town, and enjoy some organized sightseeing tours available.
Western Caribbean is big on water sports, beaches, boating, etc.
One thing you can do is take a look online at the shore excursions offered at each of the ports. This will help you determine if the activities available on an eastern or western Caribbean itinerary sound more like what you'd like to do.
Getting a penthouse will certainly give you a lot of room. Getting connecting rooms gives you the luxury of two bathrooms and lots of storage space, and some privacy as well. Having one balcony room for four people will be a lot less room than the other choices.