Used to be an iPhone fanboy myself. As someone who uses a couple of Macs for work - integration was a positive feature although it has been obliterated in recent years.
I always used to get the biggest memory I could - although I'm very surprised people are still shelling out for 64Gb versions. With the huge increases in home broadband speeds, network speeds, cloud storage I'm struggling to see why 'most' people would need anything bigger than the 16Gb. But it's your money - spend as you will.
People do realise that 24 month contracts are finance to buy the phone right? I've got an unlimited data plan on my mobile for £12 a month so if I was getting the phone I'd buy it outright and throw that sim in.