I suggest writing an email, as you express yourself well in writing. Plus it appears more thoughtful than a break-up text. Although I have sent those as well and I think they can be ok sometimes. Phone calls are good too, but I don’t think doing it in person in a good idea. Don’t drag a person out to meet you just to break the relationship off. I think it is inconsiderate as I’d prefer to be broken up with quickly and in the comfort of my own home.