I prefer Mira, based mostly on a bad experience with Triton trying to shirk its duties under the Consumer Rights Act or Sale of Goods I think it was then (had to get Trading Standards involved) a few years ago.
But I think there is a difference: Triton showers used to have 2/3 wattage at low heat setting whereas Mira seems to tend to have 1/2 wattage at low heat setting. Worth checking this detail and seeing if it is still the case!