A comparison site such as Seat Guru shows seating plans for every airplane of the major airline companies and describes the dimensions of the seats and what features they contain. The site allows you to quickly compare different airlines at the same time.
For more detailed information and pictures of airline interiors, visit individual airline sites, such as that for Delta or United. The airline websites show the seats, controls, meals, entertainment systems and services available for each class, and explain how you can improve on those levels by signing up for the airline's frequent flier programs.
For a personal and subjective opinion, contact your local travel agent. Not only can she typically answer questions, but she can base her conclusions on her own travel experiences and those of her clients. If no agents are nearby, you can search for one by zip code through the American Society of Travel Agents.
