They are both quite scenic, Murchinson is in a dairy farming valley surrounded by forested hills.
While Methven is on the flat Canterbury plains but with the back drop of the highly impressive southern alps. Methven is a sking resort during the winter so has plenty of accommodation. About 40 minutes west of Methven is the ashburtons lake and the scenery there is stunning.
The Mataura River in Southland has a excellent reputation. There are several good rivers in that area. Fiordland to the west offers excellent wilderness fishing. I have never fished that area, but I suspect the towns of Gore and Te Anau are quite central.
Central Otago also has a good reputation. There are many areas which can produce.