It entirely depends upon the sort of motoring you do and you driving style.
If you want an effortless cruiser that will eat up the miles and remain unstressed and a more comfortable ride , then go for the Roadster. You will cruise in top (or 5th on a 6 speed box) without the need to swap cogs to get the best out of it.
If you love changing down gears as you rush into corners, and a more "sporty' feel then the +4 is likely to fit the bill better.
However I am very much with Richard here, the 5 link rear suspension on the later cars does tame that rear end, and give an even better ride. The 3.7 engined cars without it can be quite a handful to drive on (or close) to the limit I am informed.
As others have said , the only way you will know is to drive both , epsecially if you do it back to back over the same stretch of road (assuming they are at the same dealer of course , a tad tricky otherwise I accept)
