By size do you mean the dimension differences between the 8 and 8+ or the storage differences between the 128 or 256?
I have an iPhone 6s+ 128GB and can't see myself using a smaller screen or capacity again. Its also in an Otterbox case so bigger than normal. Other people find the bulk offputting and have difficulty using the keyboard onehanded but I'm absolutely fine with it as I find smaller phones a bit fiddly since investing in the "phablet". My next investment will be in an iPhone 8+ 256GB (or equivalent as there's still lots of life in the 6s+, said he touching wood).