A good "all purpose" interior paint sheen is satin. It has a nice shine without looking like plastic and is very washable.
If you like semi-gloss then you should use semi-gloss. All good paints are washable and durable no matter the sheen. Even good 100% acrylic flats are very durable.
The matter of smoothness is a fact of application, not necessarily the type of sheen. Well applied paint will feel smooth. The only difference is with flat or eggshell and satin or semi-gloss, the flatter sheen's feel (look) dull and the higher sheen's feel (look) smoother.