it depends on your wireless infrastructure. If you don't have a 802.11n Accesspoint, then you don't need the 802.11n adapter. 802.11n pre-standard is around for some time and there are lots of wireless hotspots using it, but it is also backwards compatible to a/b/g.
So, if you have the possiblility to use an 802.11n infrastructure and want to benefit of the new features like more speed, then you should go for the more expensive stick. If you are not sure, which kind of infrastructure you use and if you are happy with it now, then go for the cheaper one. If you use wireless only at home to access your DSL internet connection, then most likely not the wireless infrastructure is the bottleneck