Bus or Train?

I don't think the train has two real transfers. There is major construction project underway on the rail line between the two. So you only go so far on rail, transfer to a bus around the construction zone, and then transfer back to the train. Probably easier to take the bus than mess around with the current rail situation.

Frank, thank you!
Karen

I'd be guided by the convenience of the departure time unless I had uncomfortably large or heavy luggage. In the latter case I'd definitely prefer the bus. Much easier to roll that monster bag to the side of the bus to have it stored in the hold than to maneuver it to the right train platform (possibly even down and up flights of stairs, though one hopes that isn't necessary in a city the size of Seville), wrestle it up the narrow steps onto a train, then possibly squeeze it down the aisle to a luggage rack.

If anything, the bus is likely to be cheaper.