The iPad is thinner, lighter, lasts longer on a charge, and has WAY more apps designed for touch input than a Surface, but if I had to only pick one device, I'm not sure what I'd pick.
I can and do use my iPad for almost everything I need a laptop for, but giving up my laptop and only having an iPad would make me anxious. However, I'd much rather use an iPad than a Windows tablet for my basic needs.
Fortunately, since I'm not in that situation, I will continue using an iPad as my main device, and having a MacBook Pro as a safety net.
Of course it's going to have more apps because it's been around longer and not many people realize that Windows offers a better platform with x86 computing. And of course it will last longer because it is using software that is light and child's play relatively speaking.