I work in Madang for seven months and can highly recommend it for large fish as well as the smaller stuff.
You will also find the transport easy to get around and reliable to and from the area.
Madang Resort offers good deals for xmas period as it is the quiet time. Most expats return home for the xmas holidays so you should be looking for specials. Often it is better to communicate and deal with the resort direct.
Just a suggestion, if you can't see a deal up for that period, ask for one.
Jas Aben is another resort in the Madang area and is situated in the middle of three Marine Parks.
It is beautiful but definately a different style of resort to Madang R which is situated in the main town and waterfront. J Aben did not have a dive shop operating when I left and am not sure if they have started to operate again.
Madang R has some great local staff and a manager who has been in the area for ten years. What they don't know is not worth knowing about the area and can certainly look after your needs. They also offer great deals on dive packages.
SUggest you have a look at this
http://www.youtube.com/watch?v=7VGj_aTbVF4
this is not a video but will give an idea of the area
http://www.youtube.com/watch?v=FmBARN_fh80
This is a typical day at barracudda point, also in there is magic passage.
Planet Rock is truly an amazing site as well, and not to be missed from any Madang trip with Hammerheads, Dolphin, orca, and marlin.
You will find plenty more on you tube search madang dive.......
look for the little boxes as they are from jAPanese and chinese divers.
ta
enjoy you trip
who knows may even be there in December myself