Windows by a sink should be easy to clean. Faux wood and aluminum blinds are the easiest to clean. The blinds that have smooth painted finishes, as opposed to rough, textured finishes (sandblasted) are the easiest to clean.
Black out shades are very popular, such as some honeycomb shades, and special horizontal blinds (De-Light) without the route holes are wonderful.
Humidity doesn't ordinarily adversely affect any quality window treatments, even wood blinds. However, if the window treatment gets direct water pressure, vinyl is best.
For additional privacy, consider those blinds without route holes (De-Light). If you're using vertical blinds then consider the inherent approximately 1/2 inch gap below the vertical vanes near the sill, and determine if that is enough privacy for you-especially if the window is near your bath tub.
Of utmost concern is safety. Make sure your product has the latest safety features, and that cords are not near cribs. Also be sure that if you get vinyl miniblinds that they are not the ones with hazardous lead.
Darkening the room is usually a common goal, so the are perfect. Blinds with no route holes are also fine options.
Blackout honeycomb shades are most common. Some can even be made with side rails to eliminate all light. The De-Light feature should be added to wood and aluminum blinds so that the light does not pierce through the route holes.
For a tailored look that's not too fussy, shutters and wood blinds are appropriate. Also see the related paragraph in this section regarding consistency for the front of your house.
For an elegant room, consider verticals made of sheer fabric. They are quite popular and very stylish. Many designers frequently use them to camouflage less elegant, unattractive blinds.