Here are my random thoughts. Definitely wood over glass-topped, because although a topper will protect the finish, the fingerprints will drive you insane (or at least they do for me). But the negatives of wood are that no matter what kind you get, it'll be kind of soft, so you'll either need a topper to protect it (table cover, cloth, etc) or live w/ gouges and/or water marks. So don't buy an expensive table.
And if you get an extended table (so handy!), beware the cracks where the table folds. I have a great Ikea round table that folds out to an 8 seat oval, but I bet I have at least one food-meets-crack mishap a day, so I have to regularly take a tooth pick and scrape out the oatmeal/crumbs/playdough/whatever out of there. And that doesn't even take care of the spilled drinks. So that's my next suggestion--table cloth.
I personally prefer light wood because it doesn't show smudges, marks or dust as easily. Round over square b/c it's cozier and you can fit more people around it. I've had round, square and rectangular tables and prefer round. Oh, and you might want to consider the bottom--my table's legs have a connecting arch which means my Dyson won't fit under it--I had serious crumb issues in that area until I bought a
Turkish dining table. IMO a pedestal table would be the best, but I've never seen one that extended and I like the 4 vs 8 seating option.