I have large hands and an iPhone, and I've never had never a problem typing. I occasionally hit a wrong key, but Auto Correct usually fixes it for me. My old Samsung had a touchscreen, and you could calibrate it to learn your typing patterns to allow for more accuracy. Not sure if the iPhone has a similar feature.
I don't know if Samsung has a stock app or uses the Android app, but the predictive capabilities of Swiftkey is way better than the stock app on my phone, I can't even use the old one anymore. It's one of only 3 apps I've paid for.