I've never used OneDrive but I've been a Dropbox user for a long time.
Myself personally, I'm just looking to keep all I can tightly integrated. Using services in the same ecosystem is a huge convenience for some. Sure, iCloud Drive is limited in its current form compared to Dropbox. But, I do expect things to get better down the road. I believe Apple is starting to show that they are serious about the "services" part of their business.
In short, is iCloud Drive as good as Dropbox or OneDrive? Right now, probably not. OneDrive, and especially Dropbox, have been in the marketplace a long time and have had plenty of time to iterate and grow their features. Apple did have MobileMe but I don't think anyone here wants to compare any of this to the dark days.