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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.