The best shape for a dining table is round & the best material is wood. If you’re happy with that, you can stop reading and start shopping.
The second-best shape is oval or racetrack. Our dining table is round and can be made into racetrack by adding extra leaves. (The difference between oval and racetrack is that an oval has no straight lines, when looking down on it from the top, whereas the racetrack has rounded ends and straight edges on the long sides.) The next best choice would be square, then rectangular. Freeform dining tables can be problematic. I’ve eaten at slab tables with irregular edges that follow the natural grain of the wood. At that kind of table there are often places to sit that feel nice and places that feel not-so-nice (because of the irregularities at the edge of the table caused by the grain).
The top of the table should be thick, not thin. Thin tops are problematic because they have a cutting energy like a machete. Squat down and look at the edge straight on and you’ll see what I mean. (If you want more visuals, I talk about cutting energy in this video about kitchen shelving.)
The second-best material for a tabletop is stone, then synthetic, then metal, then glass. Glass is problematic for two reasons: it has a sharp, harsh sound when dinnerware is placed on it, and unless there is a rim around the edge, it can’t be used at all in feng shui—unless it’s covered, and then what’s the point of having glass. Tables with a bare glass edge have a severe cutting energy which I firmly believe will affect you by cutting you off from reaching your goals. Beveled-edge glass is the worst because it is as though the edge has been sharpened. Once I’ve seen a glass top table with a bare edge that had no cutting energy. The glass was three or four inches thick and the edges looked like slightly melted ice—sandblasted, slightly irregular, and softly rounded. That table probably cost a mint and weighed a ton.
As I mentioned, the addition of the two rectangular leaves changes a simple circular-shaped table like ours into a racetrack shape. If there are leaves added to the table, don’t sit where a seam aims directly at you. If that must happen, use placemats or a tablecloth to cover the cracks. Here are a few example table settings. The seams run horizontally (from straight edge to straight edge) in these photos.
Oh, and one final thing about table shape—if the table is in the Relationship Corner of the home, don’t choose a pedestal table (one that has only a single, central support). Instead, use a table that has legs or trestles—that says “We are working together to support the top.”