I own both pairs of Sierras and 170ses.
THe Sierras are amazing if given the proper amplification, I mean they need JUICE!!! I'm talking 100WPC+ to bring that soundstage and bass to life.
On the other hand the 170SEs give about 90% of the Sierras even besting them on neutrality and tonal balance. The 170ses look like cheap plastic boxes but are well constructed. While the Sierras excel in Bass reach, bass control and bass power, they're almost bass heavy, and have a great world class construction and rich feel to them aesthetically, they're just sexier and classier looking than the 170s.