Maybe I don't completely understand your question.
The only thing you can really pick is the view ... garden, lagoon, or MK. I don't know what the choices are when you get moved from AKL, but these view categories are set when you make your reservation. Floor and building is only a request, not something you can guarrantee in your reservation. (Unless you stay concierge, as you will be in the Hawaii building where all the concierge rooms are.) If you pick a certain view, that may limit the buildings you could end up in, i.e. they don't all have rooms with water views, but even then a specific building is still a matter of making a request only. Same with the floor. You might request a patio or a balcony, but it's just a request.
In a perfect world, maybe you can get a water or MK view in your room switch (unless you'd prefer garden for some reason). In that case, you should decide whether you prefer a patio or balcony,as it's really a matter of preference rather than one being better, and make that request. You might also look at the maps, and decide, given your view category, which of the buildings you might prefer. Some are closer to the GCH and some the TTC. We really like being near the TTC and the Epcot monorail, but lots of folks like being close to the restaurants, etc. You can note that on the reservation as a request as well.
If you were just looking for a suggestion of our favorite spots ... then I'd pick lagoon view Tahiti with a balcony.
Regardless of where you are at the Poly, it's a magical place for a kid's first vacation at WDW, so convenient with transportation, and so many great Disney details. Have a wonderful trip wherever you end up!