I've not been to NI, but yes the scenery is breathtaking in SI.
We are heading for SI because it is a lot less populated, but at the same time there are some large populations so work prospects are still good - Christchurch and Dunedin for example

there are some great beaches and even on the westcoast where the majority are shingle it doesn't detract from their beauty and they are fantastic for beach combing. You can find some really spectacular pieces of driftwood. The rivers on SI are turquoise like you wouldn't believe!