I've had a Leupold M8 4x for quite some time, first on a .45/70 and since then on my 9.3x74R double. I've never had any dramas with it, but there again I think I've only had three scopes fail on me that I can recall (one a Tasco WC, incidentally). The fixed-power scopes do at least theoretically have the advantages over variables of greater simplicity - less to go wrong - and fewer lenses, which may allow better light transmission and lower weight, all else being equal.
The little 4x Leupold certainly seems to me to fill the bill for for a light, compact and rugged scope on a medium bore. YMMV.
