Changing sheets usually requires re-writing characters, sadly. They all use their own sets of names for attributes. You will find ardent proponents of ether of the two most popular sheets. Either one does a good job with drag and drop monsters and module monsters & NPCs. 5th Edition OGL by Roll20 is the official sheet, and has the closest integration with official offerings, as it is developed in lock step with modules and compendiums. It is clean and easy to pick up, though it lacks a little in the customization department. It is also the most widely used, if you are into the LFG forums. It also is the only D&D sheet that works with Charactermancer. D&D 5e Shaped is a user-contributed sheet that is far more complex and can do nearly anything. It can import NPCs fine, but PC sheets need to be created from scratch if coming from another source. It also has a companion script (if you ever decide to go Pro) that can do small miracles of automation. My personal preference is Shaped, because I am a tinkerer and at the Pro level, the automation is spectacular. But honestly, either sheet is a fine choice.