Overall the OT wins easily. Hayden and Natalie are unbearable. However, Ewan McGregor really is a great Obi Wan, especially in the third movie and there's a reason why Mark Hamill never got an acting career after starring in one of the most succesful films of all time... But if you weigh Alec Guiness, Harrison Ford, etc. against a couple of good actors in the prequels and an army of flat or even ridiculous deliveries it's a no brainer. The original actors had presence, the new ones lack substance or are just bad (with a few exceptions, as I said before).