I would say Jigglypuff is the easiest exclusive, after wave 4 released, it's still in stock. Jigglypuff wasn't easy to preorder, so I guess Dr.Mario wins for being easiest exclusive to order before release date.
Was 3rd in line out of 9 at Gamestop took 1 hour and 10 min for me to get my '6 bundle' & Spatoon 3-pack order through. The first person order went through 45 min after preorders went live.
online to store is a disaster...