Hey I want to develop a top down 2D game, probably with Sprites (although 3D models with a fixed camera is an option too).
I know it's not a very specific question - but generally speaking which is better for me to use, XNA or Unity?
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Simple games like you want to make do not need large and possibly slow frameworks like Unity. XNA would be better choice, as it doesn't have so much overhead, but I would recommend writing native C/C++ code with OpenGL and/or SDL instead to avoid even more overhead and to have more control of what happens in you game.