50% of photographers hate ken rockwell.
50% like him.
You choose.
Me? I hate him.
Anyway,
Get a wide angle!! If you do landscapes you'll want a wide angle. Sigma 10-20 will your cheapest option although for $700 you can't get much unfortunately that is good in all aspects e.g. Minimal CA, Minimal distortion, Minimal flare, Minimal softness, Sharpness.
Otherwise if i was you for $700 i would buy a Sigma 30 1.4 or a 50 1.4. Awesome lenses!