Long did you choose yet? I have flat feet and I had torn my ankle ligament in a street fight after I kicked a bunch of dudes trying to kill me. So I'm pretty up on sneakers for flat feet and unstable ankles.
Are there a lot of rocks in the terrain? The foot plate on the Brooks Cascadia and New Balance MT1210, 810 series are the thickest. I don't think the Salomons have an optimal good a foot plate/stability and cushion combo but I'm probably in the minority. The Inov8 don't feel cushy enough. The La Sportiva's (Raptor I think its called) is incredible, its also incredibly fuggly and will never buy a pair after trying them on and not being able to find a pair that looks like modern art.
For running, I currently have Saucony ProGrids, Asics Gel Venture 4. The Pro grids offer more forefoot flex and cushion, whereas the Asics have a thicker foot plate that protects from rocks. If you need a kick around sneaker, look no further than the Brooks Pure Cadence on flat ground. They are offset, look like they are not made for flat feet. But I was shocked that they are. For just walking around its like wearing some kind of memory foam slipper. Incredibly comfortable, although not long lasting.