I agree with BG - an ellipse may look more natural, and may be aesthetically pleasing, but they have both advantages and disadvantages.
The main dis is that the ends are smaller, so you can't fit as many people around the end (or those players are cramped.)
The long edges belly out instead of running parallel, which means players along that edge get extra space. Also, it's easier to see neighbor's chip stacks if there's a slight curve, instead of them being directly left and right of you. And, ironically, it's harder to see their hole cards when the edge is curved, because the player is not sitting at the same angle as you. These are all advantages of a round table, too.
On the minus side, though, non-straight edges are (a little) harder to build accurately, for every layer of the build, right on up to stretching your surface fabric. Also, the more your edge belly out - the farther it is for those player to reach the center. On an oval, the players at the ends can't reach, but at least the players on the edges can.
The circle is kind of an ideal from many perspectives - each player is angled away from neighbors, everyone gets equal leg room, accommodates different numbers... the main down sides are that for a table that fits 10 players, it has to be so big that nobody can reach across the center. A big round table in a small room can be difficult for people to walk around where the curves approach the walls, yet the center has a lot of "dead space."
If you room is elongated, an oval may be easier to navigate than an ellipse - because the straight edge will be lined up with the wall; you just have to leave enough space. For an ellipse, if you leave enough space for the widest point, there's an excess of space behind the neighboring seats - but if you snug it up more to avoid that waste, the seat at the widest point is going to be cramped against the wall, and that person is often expected to deal, too.
If I did one, it would be like BG says - an ovoid that has rounded ends (like a circle or oval), but instead of parallele edges, they would have a slight curve. That softens the visual lines, and even gives the players by the dealer position a little extra space (avoids getting their cards mucked as much, allows more space for bets without splashing a pot, etc.) Of course, it's subject to the room where I'm planning to put it... if it's a narrow room and the table will mostly fill it, well, oval it is.
I'd like a place where I can also fit a round table for side games and/or 6-max days.