Luckily, and without a hint of smugness, I've been fortunate enough to drive most of Britain's GT output from the 1970s as part of my day job running Great Escape Classic Car Hire. Not all of them, but enough to perhaps make a judgement call.
I love the Aston for its sense of occasion; my point is to burst the bubble a little that puts the DB6 in the rarefied world of exotica. On simple merits, the Jensen is a better car.
The big v12 Jag is a very, very good car, far better than it ever gets credit for. It handles neatly, rides brilliantly and has a super smooth v12. The problem for me, compared to the Jensen, is that it's very familiarity makes it a bit too mainstream and unremarkable. The three speed auto box is also useless, blunting the engagement, and the interior is pretty low rent on pre-90s cars. It runs a Jensen close, but no cigar. Still, buy an early one before they go intergalactic.
So there you have it, an entirely subject but frankly entirely correct assessment of the 70s GT. Now, where's my Cinzano?
We have various GT cars for hire from several locations.