Start by reading Jim’s review, then move on to these.
This bit, from Walt Mossberg’s iPhone 6 review, caught my eye:
Apple says the new iPhones have faster Wi-Fi and faster cellular LTE. In my tests, I found the iPhone 6’s Wi-Fi speeds — both downstream and upstream — were roughly double those of the 5s, and about 25 percent faster than those of the Samsung Galaxy S5.
Double the wifi speed of my iPhone 5s? That’s a huge improvement.