This is a tricky question because it's based on individual preferences. There are so many sizes and shapes of electric fireplaces that you can install one nearly anywhere in your house!
First, think about these points before the installation:
1) Allow for proper wall and ceiling clearances.
2) Avoid direct exposure to the sunlight or windows and doors.
3) Install a dedicated branch circuit from the electrical panel to avoid tripping circuit breakers.
That being said, you can add 'pop' to install one in an open stairway, the bathroom, a hallway, or the foyer. How about a fireplace in the bedroom, mounted three feet high on the wall so you can see it while lying in bed? Maybe an electric linear flush-mounted model about four feet tall on a dining room wall? Use your imagination!
Usually, the most challenging part of an installation is routing the electrical line to the fireplace location. But not a formidable one to overcome.