You wont go wrong with either machines, but I would go for the SEBO, and the E3 premium. It is a better model, has the tapered hose design so should have greater suction, is more compact and better designed than the K3 which is quite an old design now, although there still isn't much wrong with it. Those powerheads fitted to the post 2010 SEBO's are among the best you can get and do a fantastic job of agitating and grooming the carpet.
I would say Miele build quality isnt as durable as SEBO and their bags, and parts in general, are more expensive.