Some ideas to improve the touch experience of Leaflet - with regards to fingers, not pens. This could be implemented by the end-user, but having these feature available directly in Leaflet would be convenient:

• While dragging a marker, the marker should not be beneath the fingertip and thus be invisible. Instead, move the marker a delta to the top left. When releasing the marker it should should rest under the fingertip again, though.
• Polylines should have an active width separate from the drawing width, so that it is easier to click on them with a big finger.