For landscapes I think the WATE is the perfect tool. While 18 is a good sweet spot, sometimes it's not wide enough to separate the foreground. Both lenses are compact and excellent at all apertures; the only reason to stop down either is for dof. Some people use the Frankenfinder (I don't, though I have one), others use an 18mm finder; I use a CV 21mm finder (old plastic style). The CV finder's edges are about 15-16mm, it has framelines for 21, and 18 is halfway between. In fact, they used to sell it without framelines as a 15mm finder. But an 18mm Zeiss or Leica finder is a good option, too, then just adjust the lens a little wider or tighter for framing purposes.
I like to shoot by first finding the camera placement that gives me the perfect scale relationship (perspective) between foreground and background, then adjust the focal length for precise framing - this is where a zoom lens really shines. For static subjects like landscapes this is a non-issue, and lens speed doesn't matter, but you can't shoot people stuff the same way.