2.7 is the best, it doesn't take up as much memory as 4K and it gives you options to pan and zoom or crop on an image as you done convert to 1080p. The only time you'll need 4K is if you are filming for a major motion picture, or Netflix. which require 4K. Currently ALL broadcast and cable networks stream in 1080p.... One last thing if you think its cool to post your 4K video to YouTube or Vimeo, its not, as that platform will automatically set the streaming speed for the end user, and 90% of the time its 1080p, last but not least you need a 4K monitor to see a 4K image, again, most people do not have 4K monitors.