Both the F and the FA version will do. However, I prefer the 1.7 over the 1.4 for two reasons; not only for its price but also for the sharpness. The rumor goes that the 1.7 is sharper than the 1.4. Still looking.
Apparently this seems to be a question about reflections, a 1.4 with a proper lens hood is according to tests done by a pentaxforum member as good as the 1.7.
"You must use a hood with this lens to get a high contrast image out of it. The lens element is pretty much fully exposed, and is prone to flaring. A hood is a necessity with any lens, but it really stands out here compared to my experience with the 50mm 1.7, which has a recessed element. If you try this lens without a hood, you aren't really trying this lens."
"With the hood, the FA1.7 is still sharper than the FA1.4, but only marginally so. Oh yes, since the front element of the FA1.7 is already recessed, adding a hood doesn't really do much more for it."
(I'm about to buy the FA50mm 1.4 myself, new, so I've been doing some research lately too.)