What is the best way to get from Barcelona to Madrid considering cost, time & convenience in mid-November?

The best thing you can do is fly. It will take you about 35 minutes on air. In Barcelona it will take you about 20minutes train from plaza cataluña to the airport. The Aerobus works too.
If you reserve a flight now you can get a good price. The other options are by road and train. On bus it will take you about 7 hours. By train it is quite long too.

The total flight time from gate to gate on thids route is approximately one hour and five minutes.

Heavy competition on this route between Spanair and Iberia means there are usually low cost flights available, especially if you book far enough out, and on-line, with one of these two airline's websites.

It's less than five hours by train, city centre to city centre (www.renfe.es).

I agree that flying is the most convenient option in this case. To cut down the costs, try out one of the new low-cost airlines, : www.vueling.com. Flights can be purchased only three months in advance, however prices are frequently as low as 30 euros one way (+taxes).

Re: train trip. The high speed rail is
available for 3/4 of the trip. Then
the train switches to the conventional
Spanish rail. It's an interesting, fun
trip. If you leave at 7:00, you are
in other city before lunch (1 pm).
True, air may well be cheaper, but
train is downtown to downtown as mentioned before.