Car vs Bus

Okay I have two choices for transport in NZ.

1. The automacar.
2. The coachomatic.

Both have their pros and cons:
If I take the bus then it's cheaper plus I don't have to do any driving; however I will have to lug all three of my bags around with me everywhere I go, I'd have to arrange in advance which bus I'm going to take (you have to phone them up), and I'd also be limited as to where I could go.
If I hire a car it's going to be more expensive - I reckon about twice the price of busing it (petrol included). That said with a car I can keep my bags in the boot as packed or unpacked as I like; I can go where I please and pull over for photos/etc when I wish; also a car is kinda like a mobile bed when hostels are not plentiful.
Given that I originally intended to by a crap old car I think I'll plump for renting a small car for my trip. Buying a car looks like it'll cost me more than renting for the period that I'm traveling for - once you factor in MOTs, insurance, breakdown cover et al.
Renting a car has one other big advantage over taking the bus: you do not have to take the bus.