Old Mac is definitely the "funnest" course there i think.
I had the chance to play all 4 courses in December, and thoroughly enjoyed Old Mac. It gave me a whole new appreciation for the British Open in the conditions they play in!
playing Old Mac this time of the year was challenging in many ways- the grass was extremely tight and completely left me unable to play any wedges i wanted to use around the green. I ended up putting nearly everything just off the green as i didn't want to blade my 56* or 60* wedges. You never practice those shots but it was an incredibly enjoyable course.