Jaguar F-Type R
5.0 Supercharge V8
542 bhp
0-60mph 4 secs flat
186mph top speed
Porsche Cayman R
3.4 litre Flat Six Boxer
330 bhp
O-60mph 4.7 secs
It's fair to say they are both excellent cars - and a lot of it will come down to personal preferences. The F-Type is a massive step forward from anything the company has done for the past goodness knows how many years, but Porsche has improved on the Cayman since it was launched, and the new one is a far more engaging sportscar than the previous generation (which was, in itself, a fine vehicle).
Sounds a bit of a cliché, but it IS like a mini 911. In fact, in the real-world, it's almost a better option, especially if you don't want to pick up points.
Part of the thrill for me about the F-Type was the noise of the V8, but you can't buy a car based on that alone - not to mention the amount it would cost in fuel. The V6 is still a great car, but if it was me in your shoes, I'd go for the Porsche.
To be honest, you can't go wrong with either of them and, like I say, it's going to come down to personal preference. I can't understand people that judge a car on it's looks - it's all so subjective. Drive both, and make a decision from which one you enjoy the most, and can see yourself living with.
Good luck - I'm envious of you having the choice