Anything but something that requires dovetails. Especially those with windage adjustments. UNLESS you need windage adjustment due to the scope mounting holes being drilled incorrectly.
On a hunting rifle Talley Lightweights are a great choice. They are 2 piece bases with the base and lower ring made together. Reasonably priced, strong, lightweight, and easy to mount.
Two piece Weaver or Weaver style bases work well with any ring designed to fit in a cross slot. The Weavers aren't aesthetically appealing, but work and are cheap. Burris Zee rings look a lot nicer, and aren't much more expensive.
A Picatinny rail gives you the most options for scope placement and works with slot type rings.
I like to mount scopes as low as possible. A 42mm scope is right on the borderline. Low rings will work with some scopes and bases, but you may have to use medium's