Sugestion for trip to seville from madrid, bus with stops along the way for overnight stays or better to rent a car.
Neither, take a daytime high-speed train (if your goal is just to move between Madrid and Sevilla.)
It's a 2.5 hour trip by highspeed train (AVE). Other than Cordoba, there isn't much between Madrid and Sevilla that would be very enticing to tourists. It's about a 6 hour drive. I enjoyed seeing the landscape from the train, but it's mostly arid with minimal towns and cities. Actually, the landscape is not unlike New Mexico, but not as beautiful to be honest. The AVE does stop in Cordoba and it IS well worth an overnight visit. The old town is one of the best and the Mezquita is stunning.
As with the others -- AVE Madrid (Atocha) to Sevilla, with a stop in Cordoba. about 2 hours to Cordoba and another 1/2 hour to Sevilla.
i would also do the train. have a look on www.renfe.com to get the train times and fares.
Train best way to go. Your going to love Seville.
Not to start an argument, but one thing about this site is everyone is hard-wired to trains as the best way to get around. If you want the fastest way to Seville and can buy early, the high speed train is a good choice. We rode from Cordoba to Madrid just to get a ride on a high speed AVE. Busses are a great way to get around Spain, in many areas you will arrive as fast or faster by bus than train. Busses are cheap without six month advance purchase. Stops I'd recommend if you plan on slowing down and making some stops between Madrid and Seville, each would be a fairly short hop by bus: Aranjuez has a nice palace and gardens. Think of it as a smaller version of El Escorial. Toledo is a great medieval city. It gets touristy so stay at least a night to see it without crowds. I haven't been to Ciudad Real but I think it gets good reviews. Valdepenas is a nice town, the center of a major wine region but I'm not sure it has any major sights. Ubeda and Baeza were built with new world money, then became backwaters. For a nice glimpse of Spain's golden age, visit either or both (tons of olive groves in this area). From there visit Cordoba, again spend a night to wander the old quarter without the daily tourist crush then on to Seville. Alternatively from Ubeda or Baeza, visit Granada, Ronda, Gibraltar, Tarifa, Jerez and on to Seville. Yes you will love Seville - Spain has a lot to love.