The c63 is a bit Tail happy for me.. It's nt a car I'd feel relaxed driving. The ride is rock hard and some of the interior on the c class (which is a lower end car than an xf) feels. Bit low rent. The xf is better built in terms of interior spec, and is a much smoother car to be behind the wheel of. It's the one I'd choose for sure. I find the c63 just a tiny bit vulgar.
Bear in mind jaguar will be going aluminium platform on the xf soon, and that's likely to be superb, even with the same engines