confused

im going to get a receiver this week and it looks like its going to be a sky f3 but im confused as whats the difference between the f3 f5 open box 9,10,11 and skybox m3,can someone advise me as to which is the better box im assuming the higher the number the better the box but most peeps say the f3 is the one to get :grayno: than you in advance
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the f3 m3 or f5 has a better layout of a channel list and features ovr the x series stuff