I would strongly recommend Wicker Man! Being the newest ride, it will demand some of the longest queue times but using the ridetimes.co.uk will help you.plan your day. Sometimes the queue will drop to 40 minutes or so. If you see it at this, or below, then get in line!
I'd recommend going to Forbidden Valley first as it is usually dead at 10am and usually the hour after. Work your way to Dark Forest and then X Sector. This way you are going against the crowds!
Have a great day