I'd be more likely to go with the Polynesian again. But I also don't think the GF is too "frou-frou..." I mean, it is beautiful, but I don't think it's as nice as some other hotels I've stayed at. (Caesar's Palace in Las Vegas was much more plush than the GF).
ANYWAY, with that said, here are some comparisons of the two:
POLYNESIAN
1. Proximity to the TTC - very convenient. You can walk to the TTC to get the monorail directly to EPCOT. At the GF you have to change monorails at the TTC.
2. Restaurants - I think Kona Cafe and O'hana are two of the best restuarants in WDW!
3. Love the pools and the fact that you can lie on the beach and look at the castle.
4. Casual and laid back feel throughout the resort.
5. Beautifully landscaped grounds with a tropical feel.
6. Separate game room and kids center.
GRAND FLORIDIAN
1. Good choice of restaurants - 1900 Park Fare has great character meals.
2. Magically themed rooms like Alice in Wonderland and Wind in the Willows.
3. If you have a lagoon view room, you can hear the sounds of the MK.
4. Transportation is good - but you have to switch monorail trains at the TTC to go to EPCOT.
5. 24 snack shop can get crowded and loud because all the video games are in there, too.
I guess my personal opinion is that the Polynesian is more kid friendly. I have seen TONS of kids at the GF both times I stayed there, but I still think I'd go with the Polynesian. Plus I think the rooms at the Poly are a bit more roomy than those at the GF.
Maybe you'll get some other opinions. Also, I don't have kids (yet - #1 is due in August), but even so, I still think I'd go with the Polynesian with kids.......
Hope this helps! Have fun planning!!!!!!!!!!!!!!!!!!!!!!!!!