On our last trip in October, we dined at both restaurants.
Yachtsman's Steakhouse is a very crowded restaurant. The tables are very close togehter and the waitress was always hitting our table going by, as were the other Cm's going to their tables. They brought the wrong Entree out for my DH and we had to return it and wait longer for his food - I was finished eating by the time he got his food.
LeCellier has always been awesome. Been going there for several years and not a bad thing to say about it. Of course, you need to get into Epcot to eat there, if you are not in the park already.
My vote would defnitely be LeCelier.