Tom Kelly,
If you have a car and you are staying in East Lothian then there are over 20 courses within 15 mins drive of North Berwick. From what I've read in this thread I would certainly play North Berwick again. I must have played/caddied/walked the course over 1500 times and I still find fun ways to play new shots all the time.
Then, as ever, it comes down to personal preference. If you are after what people would generally accept as links then I would opt for Gullane No. 1, Gullane No. 2 (some of the holes on the back 9 here could be the best golf on Gullane hill, the front 9 is so so), Luffness New (the most interesting greens of the courses listed, plus good bunkering) and Dunbar. My choice would be Luffness and Dunbar but its Coke versus Pepsi comparing them to the two Gullane courses I listed. They will all quench your thirst for good golf.
Kilspindie is a personal favourite and I like Longniddry as an alternative round in generally links style conditions, along with a treelined element. The Glen is a nice walk and not to be dismissed on the grounds of being a little bland. You will enjoy your 18 holes but dont expect to come away with any great insight into green contouring.
Muirfield is actually good value at this time of year and its in great condition at the moment. Good luck trying to walk it! You might be able to walk through it to "get to beach" but I would advise against taking any liberties, even with the best intentions.
Goswick is about an hours drive from North Berwick, near Berwick itself. (not to be confused, it sounds pedantic but no local would EVER call North Berwick, Berwick) I really like Goswick; its dirt cheap and present great value for what you see. There are a handful of really cool holes mixed amongst some good holes and a few very ordinary ones. This would be the tier below the ones above but above the likes of Winterfield, Whitekirk, Royal Musselburgh, Musselburgh, Musselburgh Old, Haddington, Castle Park, Gifford and even Craigielaw.
I could give a pretty good read on Fife too but there are guys better placed to do that. Elie is my favourite on that Forth coast but the New is my personal choice outside of the headliners in and around St. Andrews. Scotscraig is a little further North of St. Andrews - decent but I havent played there for 10 years.
Have fun!
Simon