Hi Mark,
I like the older Porsches, but not so keen on the newer ones. They're (in my opinion) just a little to clinical. Sort of point and shoot really. I had a couple of Porsches in my late 20's which I really enjoyed, and then bought a 911 4S cab about four years ago and it was a great car, but I never loved it. Very fast and secure, but I always felt the car was driving me as opposed to me driving the car. They are brilliantly engineered and have superb electronic gizmos, but I just never fell in love.
If I was looking for a daily driving sports car I'd go back to one, as they tick a lot of boxes, but as a weekend fun sports car I'd sooner drive the BMW's. They (to me) have a lot more feel and soul. I have a Z4M which on a track is just great fun. The Z4 is a really stable platform from which to have fun. It drifts away a treat and feels very capable. The Z8 I've never tracked, but it is balanced and so well made. It's also just such a pretty car. Understated and relatively unknown. I like both those attributes.
Horses for courses as they say. All depends on what you use the cars for and what you want from them. But the BMW's are definitely an awful lot cheaper to own and run than a modern Porsche. Every trip I had to a Porsche dealer for service was eye watering!