Must admit I am tempted by the Supra as a next car, they are knocking on a bit now so you will need to do some work on them to get them up to what we might consider to be more modern standards - they can look stunning though
It is a 20 year old design, I would expect in ten years time there will be plenty of people saying how out of date the 350z looks.
The engine though is stunning and reliable by modern standards, if you like a tinker, you can put a lot of power increases through it at a low cost. Handling wise its easily improved with some strut bracing and coilovers.
350z is the safer bet probably more comfortable and better on the petrol mpg, Supras are a lot rarer and a bit different with plenty more speed.