Thank you all for answers. About resolution, I must say Paperewhite also have a 758x1024 resolution. Furthermore for Paperwhite Amazon reports pixel density, Kobo on the contrary is a bit lacking in reporting
tech specs...
The only problem of Paperwhite for what I read is its light can't be turned off completely and it have not an epub support (this is more a thing that I dislike very much that a real defect ^_^)