If you are planning a second trip in the same year to Disney then I don't think it matters which way you go on the first trip.
I'm assuming you don't work your job on weekends. Anyway, if you count two weekends you actually have 9 days without using anymore vacation time. This doesn't even count Friday night. If you plan the vacation, you can have all your luggage done ahead of time, etc. Based on this, you can have more time at the parks, if your budget will allow it. You can do this at the front end of your trip or the back end depending on your dates. Now, you may have to work out some transportation issues, but it's doable. Another consideration is you will probably feel a little tired going back to work without some extra time to adjust back home.
If your budget doesn't allow it, then you have to decide what's more fun for you and your family. Cruising is very different from doing the parks. It's a different pace, too. If you have done the parks many times over then I think the cruise experience will be more enjoyable combined with some time at the parks. If you really plan hard and wise, you can probably get more out of the parks then a usual stay there; so, you can make up some time by just having a better plan for the parks.
The activities on a cruise are very different from being on land at the parks. You need to check it out very thoroughly and see if the cruise activities sound appealing to you or not. If you like thrill rides to the nth degree then I'm not sure you will like a cruise, as much as, the parks.
Although cruising is special with the Disney theming, etc. you can get a much more affordable cruise trip going with another cruise company. If finances are not an issue then this won't matter. I don't need to be on a
Disney cruise line to have a fun cruise trip. I'd rather take two trips and not mix the two together. You can take a
Disney cruise by itself, too. I think it can be more tiring trying to combine both for the same trip.
Any vacation is fun; so, just decide what you may like more and do it. Enjoy!