It really boils down to what is best for *your* family. We've stayed there 3 times. Twice in a Lion King suite (once in each building) and once in a Nemo suite (building 5). The most important thing to us when choosing the location is that we're close to the food court and bus stops. We use the refillable mugs a lot (at least 3 times a day) so we don't want to have to walk too far to do that. We also come back to the room every afternoon for a break and go back to the parks at night so we use the buses a lot. While being close to a pool is nice, we didn't find the walk from the LK buildings to be a problem (our rooms were at the end of the building closest to the main building/Nemo section each time) as we usually only swim 4 or 5 times during our stay. We've ruled out staying in the Cars section as most of that area is a longer walk to the food court and bus stops than we prefer to have. Keep in mind that the food court and bus stops are at the end of Animation Hall closest to the Lion King buildings so even though building 1 of the Cars section is close to Animation Hall, you still have to walk the full length of the building for the amenities. And building 2 of the Cars section is the furthest suite building from the food court and bus stops (though most of the Little Mermaid section is further). That being said, I do think the Cars area has the best theming especially at night and we always walk over there to soak it in one night during our stay. If you have kids that love the Cars movies, it might be a good choice...though I would definitely try to get a suite at the end of building 1 or 3 closest to Animation Hall.
We've enjoyed our stay in all 3 of the locations we've been in but I think our favorite was the 1st floor of Nemo building 5. It was convenient to everything we needed and we didn't need to use the stairs or elevators at all (our LK rooms were both 4th floor). If you plan to drive to the parks, I would suggest a Lion King (or Cars) suite over a Nemo Suite. We drive to Disney but use the buses once we arrive. I needed to go to the car twice during our stay when we were in the Nemo suite and it was a HIKE! If we were using our car frequently during our visit, I would not stay in a Nemo suite -- it would be LK all the way. Both times we stayed at LK we were able to park right across the driveway (first or second spot) from Building 10.
And as far as the "brightness" of the rooms -- I was really concerned about that the first time we stayed there but I found that once we had all of our stuff in the room, I really didn't notice it.