You can request a certain area (we emailed DC in advance of our visit to request that we be placed near the Wind Away River and Freshwater Oasis, our two favourite areas in the park) but requests are not guaranteed. They do do their best to honour them, though.
Our cabana, near the entrance to the river, was a short walk to the Laguna Grill but not super close (I don't think any are really, really close to the restaurant as it wouldn't be very quiet there!).
A good location is very subjective. Some will want to be close to the Grand Reef if snorkelling is your thing to do. Others will want to be close to the dolphin pools so they can watch the dolphin interactions. Others, like us, will prefer the lazy river area. It just depends on what your family enjoys doing the most. For our first cabana rental, we let them pick the location....for our second rental, we requested a specific area. I will say that those cabanas near the Grand Reef (where we were assigned the first time) have a great view of the snorkellers but its a fairly lengthy walk to the Laguna Grill.