I see very little difference between Endless and Zappos, except:
-Endless has a LOT more brands, including brands that Zappos used to carry but has now discontinued
-Endless often has more styles within each brand
-Endless still has a 100% price match, which Zappos discontinued
-Zappos' new site drives me crazy
-Zappos' idea of a "sale" price is laughable. 10% off a pair of $160 shoes does not leave much of a dent. Endless always has regular sale and clearance prices, in addition to other sales and promos.
-Their customer service is at least as good and helpful as Zappos'
Hence, I prefer Endless. I have been using Zappos since I was a tot of 15 years old. I'm not kidding. I still remember the first pair of shoes I bought from them: a pair of Sketchers ankle boots that I bought with my mom's credit card (with her permission of course). Those were the days!
I have never had an item from Endless that didn't ship with free overnight shipping. That seems very exceptional to me.