I got a 360 prenium about 4 weeks ago and have been using the microsoft wireless adapter, which installs easily - plug it in and go - although it has stopped working twice and needed to be unplugged and plugged back in ( a pain for me as my 360 is tucked away in a hifi rack). The performance on the microsoft adapter seems at least comaparable to the netgear card on my pc and is totally fine for online gaming, however streaming movies takes a few seconds to buffer and scanning through is tediously slow.
Using a router / range extender is definitely an option, but the hassle of setting it up can sometimes be difficult, i suspect it may be less reliable than the microsoft solution and there is no performance to be gained unless you use two MIMO / 802.11n routers - which would be expensive.
The good old ethernet cable is the cheapest, fastest and most reliable method in my opinion, however another option to consider may be a home powerline networking solution - I'm looking into this at the moment connecting one to my router and one to my xbox - unless I win the lottery tonight; then its a new house with more CAT5 than you can imagine....