I would like to know what is the best way to water potted (plants),

Water with a watering can, water from the top until it runs out the bottom,
then don't water again until it starts to dry out. Water African violets by
putting the spout between the leaves.

either the soil stays too wet, or it dries out too much,

If the soil stays too wet, repot in a more open mix, with added sand or
Perlite. If it dries out too much, you may need to repot in a bigger pot or
water more often.

This causes the top of the soil to get weird though, it is almost hard, and
coated, not soft and slightly airy like below the surface.

That is the fault of poor soil, not the watering method.
You can't water plants on a time schedule. You must water thoroughly. The
timing depends on the size & needs of the individual plant.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)