Which one you chosen
 

If you could chose for yourself, A 8 inch thick cock but you only last 30 seconds, or a decent 6 inch and last 15 minutes.

8 inches, without a doubt. You could learn to last longer (maybe jerking off before the sex would help). You can't learn to grow a couple of inches.

I can last forever and a day at my age (early 60s), but I'd happily shoot much sooner for just one more inch added to my 4-inch weenie.