4G is patchy at best. When it works, it's amazing (i.e. it worked well for me on the rooftop of my office building while I tested streaming Netflix - rocked it). But most of the time, it doesn't work that well. Leave 3G on all the time and turn on 4G if you can't get 3G and/or if you want to boost the 3G data speed in an area that gets 4G speeds (which, in my case, seems to only be on rooftops, midtown!).
Sprint told me today that 4G "should always work" but they're delusional - it doesn't. At least, it doesn't for me.
I personally prefer Wifi at home (no hotspot, just right off my home network).