I like the 4.2

 

They are both fantastic engines & have that fabulous Jag V8 "roar"
If you're in the UK, the insurance works out a little cheaper on the 3.5 but the fuel consumption for both engines is virtually the same. I'd say go for the 4.2, the extra performance is worth it - these cars really move.
You can cruise along safe in the knowledge that if anyone overtakes you, it's because you have chosen to allow them to do so.

 

Thanks for your reply the 4.2 it is