Which global variable do I use?

Do I use a numbered global variable or a text global variable for a level select screen? I made a level select where the player can choose which level to do - no locked levels - and now I want to change the level sprite when level is completed.

You should be able to use either. It's all about implementation.

Suppose each level has a number, then you can simply check for globalvariable = level.number and go to that level.

If you want to name the levels, then you can do a similar check: globalvariable = level.name