I've driven both a 2.0 Veloce and a 2.5 Veloce today. The 2.0 feels more chuckable and better balanced than the V6. V6 counters this with better engine and performance. Sport Pack/Veloce 2.0s are not significantly better handlers than cars with standard suspension however I would say that Sport Suspension is a must on the V6 to counteract the heavier engine.
If buying a V6 leather and sport pack are essential for resale, on 2.0 look for Sport Pack and/or leather as standard cars are hard work to sell on. Avoid Achille Blue, Amazon Green and Africa Grey.
2.5 is more reliable than 2.0 - less propensity to snap belts, more consistent oil consumption, no variator, fewer plugs. However 2.5 is 5mpg worse and more to insure and more to service.
On V6 listen for belt tensioner wear and check gear synchros as the electronic throttle can lead to clutch slipping and rushed changes. On 2.0 listen for cam variator. On both cars check front edge of roof for rust, noisy front suspension, condition of carpets, air con performance.