I've always found Dropbox to be fast and reliable, which hasn't always been the case for Apple's cloud services. Unless apps start removing Dropbox support, I think I'm going to stick with Dropbox for now.
1TB is actually too big for me. My MacBook Pro only has a 512GB SSD.
Not sure whether I'll switch from Dropbox to iCloud storage. Dropbox is better value but I think I'll wait and see how seamless the iCloud experience is before deciding.