I like 2 piece bases. If the 2 piece Leupold Weaver Style base is used on an accutrigger gun the bases are both round bottomed and are interchangable.
Concerning rings the best extension rings I found are Millet Weaver Style Rings
which work well, though their adjustable windage is sometimes a bother.
In a few years when the dust finally clears and people start counting their change there is a pretty good chance that President Obama may become known as The Great Absquatulator
. You heard it first here on TFL.