It looks like some people are talking about the 8 + 8 Plus as a single model, and others are talking about the 8, and the 8 Plus, as separate models.
The sales guesstimates (since Apple does not break this down) are:
- iPhone 8: 24 percent
- iPhone 8 Plus: 17 percent
- iPhone X: 20 percent
- All other iPhone models: 39 percent
So the X has outsold either 8 model. I don't see how you can lump the 8 and the 8 Plus together for these purposes. They are two very different phones. Physical size foremost, but also the camera and battery life significantly distinguish them. I had a 6S Plus for a while and it was completely unmanageable in my daily routine. I don't think there are very many people would would be happy with either.
Apple's iPhone lineup this year is a surprisingly large mess, from a consumer's perspective. SE, 6S, 6S Plus, 7, 7 Plus, 8, 8 Plus and X? Eight different phones. In prior years, there was the SE, then last year's two phones, then the current year's two phones. We have three new phones this year and five hangers-on.
Look at the chart in this article for more:
https://www.macrumors.com/2018/01/22/iphone-sales-breakdown-4q17-cirp/