a couple years down the road, I'd vote for three.js because
ie 11 supports webgl (to what extent I can't assure you since i'm usually in chrome)
and, as far as importing external models into three.js, here's a link to mrdoob's updated loaders (so many!)
UPDATE nov 2019: the THREE.js loaders are now far more and it makes little sense to post them all: just go to this link
http://threejs.org/examples and review the loaders - at least 20 of them