This is simple:Netflix Box If: you already have netflix, plan to get netflix, and understand that their streaming slecltion is rather small right now but have been getting larger since the roku box came out. Also will be able to do HD once netflix starts streaming HD.
Apple TV If: You want a larger selection of movies to rent or buy and/or plan to rip your own movies.
Xbox 360 If: If you want to game, rent or buy movies online, rip your own movies, large selection of movies. Also the 360 will let you stream netflix movies and handles lets you manage your queue.
Personally if you want spend the least amount of money the roku box would be the best way to go.
R.I.P. FEAR
It drops deep as it does in my breath
I never sleep, cause sleep is the cousin of death - NAS
I take 7 MC's put em in a line
And add 7 more brothas who think they can rhyme
Well, it'll take 7 more before I go for mine
And that's 21 MC's ate up at the same time - Rakim