I have a Voyage and all three models of the Paperwhite. I use the Voyage more than the Paperwhites but I also use the 2 latest Paperwhites a lot. It generally amounts to using whichever device has the book that I've decided to read. If none does I usually pick the Voyage and put it on that.
The reasons I prefer the Voyage are 2: I like the power switch on the back and I like that it's smaller and lighter. Well, if I have to keep it in my pants pocket then that means using the Voyage, depending on which pants I'm wearing. It'll fit in all of my pockets. The Paperwhite will fit in about half of them, maybe a bit less than half.
For a long time I also preferred the flat bezel on the Voyage but little by little I've realized that the inset screen makes it easier to avoid accidental taps when my focus is on the book and I'm being a little careless. Now I think I prefer the recessed screen.
I have to say, though, that all of these are very small differences. Honestly I don't care a lot which one I'm reading with. If anything were to happen to my Voyage maybe I'd get another one. Maybe I wouldn't. I'm really not sure.
So, regardless of Dr Drib's advice I'm going to tell you which is the better reader. It's whichever one you feel like getting.
By the way, I've never owned or even seen an Oasis so I've left that out.
Barry