Do you think size is a better upgrade than performance?

I have a budget for an iPhone 8 or iPhone 7 Plus and was wondering what you think would be a better upgrade from an iPhone 6s.

Size should never be priority over performance. I'd much rather a faster and more reliable phone than a bigger one.

Phones often have speed in nanoseconds. On my best days, I can't think or move even in milliseconds - but i sure do appreciate a bigger screen. I will NOT buy a glass case until these have a better track record. In 2018, we will upgrade our iPhone 6 phones to 7 plus. The difference in price and future screen replacements will more than pay for all the single malt Scotch I intend to buy with the savings.