Another vote for "neither, but 24mm if you really want one of these f/1.x primes".
I've gone from wide zooms (favorite is the Tokina APS-C 11-16) to 24mm equivalent prime only (the m4/3 12mm f/2) for landscapes. This isn't so bad, but I often wish I had an option of going to 20mm, sometimes even wider. Beyond versatility, a zoom would be lighter and cheaper than the 24mm, and the wider aperture of the 24mm f/1.4 is IMO only really relevant for low light action shots in crowds and such (though if people disagree I'm open to other views).
I also don't view 28mm as a landscape focal length - not bad (I often use an m4/3 14mm f/2.5 for non-landscape), but if I do wide landscapes I want wider.
Any lens can be your landscape lens as long as you know what you're doing. For example, you can stitch a few shots into a pano even if you don't carry a tripod.
If you are even considering spending that much for the 24mm f/1.4 for landscapes, you are already better off getting a Zeiss 18 or 21mm. Don't fear the manual focus on a ultra wide lens. Plus if you find a used one, you can likely sell it for what you paid.
And I second what mshi says. The 28mm would make a nice wide angle walk around lens in tight places. If you have to go wider for landscape shots, get a pano head. I've shot very wide angle, crazy detailed mosiac images with a Canon 350D and the $90 Canon 50mm on a pano head.
