The size I've preferred for some time is 5x7. Enough room to get pretty creative. I like to make the card base from kraft, then cut down a slightly smaller pattern paper panel so that there's a narrow kraft edge (looks more finished). Am using all kinds of stamped images on top of the pattern paper, a lot of them fussy cut, sometimes colored molding paste through stencils. Want to do more on watercolor paper with stamped images inked in Versafine and embossed with clear ep.
Molly