It's not an easy answer as both cars are different creatures - although they're both retro-styled and fairly lazy. For our money, we'd go for the S-type - but the only way you can really answer that question is to drive both. Remember, these cars are getting on a bit now so they won't handle as well as they did fresh out the box. You might find a low-mileage Rover 75 that you prefer to a more leggy Jaguar. Of course, you could always go for a Rover 75 based MG ZT - they inspire and attract enthusiasts and have excellent club support.