I was advised that if the tile is going on the wall (backsplash for kitchen, but I think this would apply to walls in a bathroom as well) that it didn't matter so much. But, for my bathroom floor tile, I was advised not to go big box because my installer didn't think the quality was as good and you want something you'll be walking on to be really solid. Made sense to me, but I'll be interested to hear what others think...

beth's is a good rule of thumb.

Whenever I think about the quality of a tile I think of my really cheap Chinese black marble tile I bought for my powder room. I got it from Lowes and returned 2/3 of the boxes because tiles in them were made of seamed-together marble scraps. They would have been difficult to lay properly, impossible to cut. It took me 3 trips to get enough acceptable boxes. But I'd read the reviews, knew what to look for, inspected every tile in every box before I left the store, and in truth, once it's down, it's down. Cheap tile can be more difficult to work with than the good stuff.

But don't confuse cheap with inexpensive. You're going to be using machine made, mass-produced ceramic subway tile. It'll be fine.

Totally agree with the above posts.

is there a significant loss in durabilty when going with the big-box American Olean or the like versions?

Nope. You will get a very uniform product - they have production and QC under tight control.

And if you want durable bath floor tiles, the hex porcelain from Dal-Tile are fabulous. Use white with a medium grey grout.