What's difficult to learn: windsurfing or kite surfing?

Take lessons from a qualified instructor in both cases, but especially kite (safety).
You can stand on a windsurfer almost immediately, the learner gear is really friendly, so if you want progress in 2–3 hours maybe windsurfing.
Kiteboarding is a little slower, but you progress more quickly to planing etc.
So generally windsurfing is a slow long progression of learning, kite is shorter and steeper.
Kites are easier to transport, but suitable places to kite are less common.
Windsurfer, more gear but more places to sail.
You can stand on a windsurfer almost immediately, the learner gear is really friendly, so if you want progress in 2–3 hours maybe windsurfing.
Kiteboarding is a little slower, but you progress more quickly to planing etc.
So generally windsurfing is a slow long progression of learning, kite is shorter and steeper.
Kites are easier to transport, but suitable places to kite are less common.
Windsurfer, more gear but more places to sail.