A lot of this decision depends upon where you have gone before, where you would like to go now, and of course, how much time you have available.  We have been to Cabo and Ensenada before (a five day on the Elation...just loved it to death)...so we are now opting to take the eight day cruise on the Spirit to Acapulco, etc., in Nov 09 since we have not been to any of these ports yet.  Still on our list is the seven Day to Puerto Vallarta on the Splendor, hopefully in 2010,....Theses ports will all be new to us (exception Cabo) and our friends from the east coast are looking at joining us....so we would have the best of both worlds.

Best of luck and wishing you great times and of course FUN, regardless on the cruise you choose.

One more thing.....

 If embarkation location is a factor (based upon where you live/distance for travel/expense/etc.) then consider the eight day Spirit leaves from San Diego and the seven day Splendor leaves from Long Beach.  Although some may consider location as unimportant, others may use it as a "make or break" factor.  Time to spend in the area before or after the cruise may also be a factor....both of these locations have a lot of activities, so...whatever works best for you, your family and friends.

 Once again, have FUN, regardless of what you decide.

Opinions. Hmmm.

If you're talking about the Splendor Puerto Vallarta/ Mazatlan/ Cabo versus the Spirit and its Acapulco/ Ixtapa/ Manzanillo itinerary,my opinion is that the Splendor is likely to provide a bit more for the kids. You can see below that I'm actually doing both, the Spirit because it's cheeeeep for a New Year's Eve cruise and goes somewhere we have never been (The GF's been to PV and both of us have been to Cabo, me many times).

Inexpensive shore excursions? Not many on the list that are inexpensive. You should try shopping on the internet, there are plenty of companies that will undercut the cruise ship rates. Buyer beware as some of them undercut service as well. Your best bet to keep the expense low is to try to formulate your own nature-type tour, either on land or in the water or a combination thereof. Some of the ports are more accommodating of that - again I think the ports of call from the Splendor have the edge for that.

~ MattInSoCal 

We are on the Spirit in October from San Diego. Not crazy about the Manzanillo stop but we have a group of co-workers going so this made it easier to gather everyone together. If I had my choice, I would take the 7 day one. Our last trip to mexico was a 10 day on Holland leaving from San Diego. Talk about not wanting to go home.

I could be wrong, but I think the Spirit does Hawaii during spring bread, not Mexico.  If you are planning on going during spring break I think your only choice will be the 7 day.