Both will be about the same in terms of close to those several locations... you will not go wrong with either put it that way! Wellington city center is small.
Copthorne closer to Te Papa (3 mins brisk walk)... and a bunch of cafes in Oriental Bay and in the Courtney Place end of the city centre (2 mins)... There is a bit less cover walking from Copthorne if it were raining a lot. And a short walk of say 2 minutes to the bus stops if you wanted to bus back towards the Lambton Quay shops from Copthorne. I guess the difference is this one's near water so has some nice views and aspect for afternoon sun.
Novotel is more city-business district-ish. May have view of sea from some rooms. And then Novotel is close to Lambton Quay cafes and shops - literally the elevator ride! That's then an undercover area so handy if it's raining. (we're having a wintery spell right now!). So to get to te papa from there, either a ten minute walk along mostly shop (covered) then dash across the roads to the waterfront - or bus and then the dash across road from a few bus stops nearby.
Here's a good wellington website looks very up to date: http://www.wellingtonnz.com/