Probably whichevers cheaper? It depends on how close to the screen you sit, don't get too big if you are sitting close.

Screen Viewing distance range
26" 3.25-5.5 feet
32" 4.0-6.66 feet
37" 4.63-7.71 feet
40" 5.0-8.33 feet
46" 5.75-9.5 feet
52" 6.5-10.8 feet
58" 7.25-12 feet
65" 8.13-13.5 feet
70" 8.75-14.75 feet
Note: This chart should not be used to determine screen sizes for front projectors. See our front-projector screen recommendations for more info.
Random google, don't know if it's reliable.