Um...why not split them?

Quads are great.  Tris are okay, especially for non-organics (they don't have to bend).  Just avoid asterix's as they can sometimes show up in renders.

I should add -- quads whenever possible is good for Carrara, too.  As of version 6 (or was it 5?) when you increase subdivision it does so with quads.  But even more importantly, Carrara's line tools are not very smart about tris.  Make a bevel or just extract an edge and it may get "lost" around the corner of a narrow tri.  Quads don't have that problem.