Dances listed in order of difficulty
Level 1 dances are really easy, the very easiest being perhaps Circassian Circle, Four Around Four and Blaydon Races. Any dance using reels, ladies chains, or rights-and-lefts is automatically at least level 2; more debatably, I have put all waltz dances at level 2, likewise dances with moves that will take time to explain. Levels 3 and higher are quite guessy.
Sometimes the dancers you're calling for will want easy dances because they're not experienced, and sometimes they want easy but energetic dances so they can work up a good sweat. Other times the dancers want something that will make them think a bit, or something that will let them display their elegance. Up to you to get it right for the people you meet on the night!
Always have ready some easier dances, in case the group isn't as confident as you expected, AND some harder dances than you think you'll need - if the group is more experienced than you expected, it's embarrassing to have nothing suitable.