I did the North-south from St Malo, detouring west on the Loire, for the castles, then back to the coast, veering inward for the Tourmalet + Aubisque, up to visit Toulouse, veering back south to Carcassonne and the coast around Narbonne then onto Augues Morte. Then train to Nice and chuck the bike on the plane (strap on bits of volvic bottle, cardboard, flip flops, then into two 4 euro Nice airport poly bags) back to rainy Scotland.
Somehow this all took 28 days. You lot must've been flying along to do it in 5 days or whatever. Mind you, my unplanned route was very zig zaggy!
Advantage of North south is that you hit the hills when you're fitter and you can use planes w/o so much bike safety worry (but w/o so much ability to use a big cardboard box).
I really enjoyed the ferry and might detour for the Santander / Bilbao ferry home sometime. I'd consider a straighter line from top left to bottom right followed by gorges and mountains along to Santander and a relaxing 36 hours on the boat home, feet up all the way.Not as cheap as the plane though.
I like heading south so that any spare day at the end is warmer.