Hatchback or not - it does not makes a lot of difference. I would go for doors and install speakers there. After all car manufacturer specifically designed so. When choosing the speakers make sure they fit depth-wise, some might have too big magnets on them.
Having speakers in my doors for 16 years now - they work perfectly, no corrosion whatsoever. The only quirk are the wires - you need to make sure they don't obstruct windows going up/down. (I had windows and locks replaced a few times and each time I assembled the door I discovered that wires were in a way of a window, had to redo)
Speakers in the boot are usually complementary to the speakers in the front, they add more power and surround sound effect (when properly balanced).
EDIT: Sound quality highly depends on speakers and amp. There are multi-band speaker models that employ up to 3 speakers in one (tremble speakers installed in front of bass). They generally sound better than single-band speakers. Some models go in pairs, each side has a main 6" speaker and a small 1" twitter that is installed separately (under the side mirror or someplace else). Spend some time in a shop listening and comparing speakers to each other. Make sure your amp has enough power for the speakers and your wires are thick enough to carry it. Professional audio specialist might give you a better advice (sound dampening, amp choice, etc)