If you "need" an SUV that can go off-road, the Countryman doesn't have great ground clearance, it doesn't have four-wheel drive or even all-wheel drive (and the base Countryman, which is all you can get at the same price as the Explorer, doesn't even have a limited slip differential) and it's not flood capable.

The Explorer can ford up to three feet (estimate based on air filter height) of water, has three off-road modes, tons more interior space, more power, seven seats, a wash-and-wear interior, and it doesn't drive too badly for a 2.2 ton SUV. While the Countryman S is just as quick with a much smaller engine and handles better, that's not a convincing argument if you're comparing the two as go-anywhere do-anything SUVs... not that you'll be doing much off-roading with the stock 20" wheels on the Explorer...

The Countryman's more natural competition are the Lexus RX and the BMW X1. The Explorer's more natural competition are the Pajero, CX9 and Veracruz.

I really like the Explorer, but it's not for me, because there are only three of us in the family, which means I would consider the Countryman. Because I don't need the space.

But if you really don't need the space, the Cooper S is even more convincing at the same price as the base Countryman.