<<<any advice in general about where is best to stay is much appreciated! =)>>>
Are you travelling alone? I assume you're female by your handle, which only matters if you are averse to staying in areas that may bring unwanted attention.
Shibuya is a nice area but lacks a lot of hotel choices. Shinjuku is better for hotel choices but it is much less refined than the Ginza. If you're budget constrained, then the Shitamachi (downtown, Ueno, etc.) area is probably best. If you're into staying out late, partying, clubbing and having a good time then Roppongi or Shinjuku is probably your best choice. If you're an early riser and prefer to do a lot during the day and take it easy at night then other areas are probably more optimal. If you want something convenient to Yokohama and JR transportation then Shinagawa is probably best.
So basically, if you can profile the following things, a better assessment can be made: gender, age bracket, interests, dislikes, room size preference (small is OK or not, etc.), budget considerations, dining preferences, planned activities, excursions planned, mobility (can you walk significant distances without tiring), etc.
If you're coming from Sydney, then you won't have jetlag issues so that part should be simple.