Renfe's long-distance train has two types of seats, and three classes, or categories of ticket. It's confusing.
Seats:
Basico, or 2nd class seats are perfectly comfortable. Arranged as 2+2. Wider and more legroom than coach on a plane.
1st class seats can be sold as either Confort or Premium. They've got a 1+2 set up, and are wider with more legroom.
Tickets:
Basico has is the most restrictive, less flexible fare, with 2nd class seats.
Elige fare are more flexible. 'Elige Standard' will be in 2nd class seats. Or pay more for 'Elige Confort' in 1st class seats.
Premium fares are the most flexible, always 1st class seats, with lounge access and food service included.
*Some trains don't have food service offered, in which case 1st class seats will be only be sold as Elige Confort
*Only 2nd class seating offers a formal Quiet Car. The 1st class cars are less dense and have fewer families, so are quieter than normal. But you could still get stuck next to someone on the phone.