GNOME3 doesn’t do the best job of handling monitors of a different size, especially when they’re setup vertically. Having said that, it’s almost a perfect user experience if the larger monitor is setup as the primary. When the smaller one is primary, at least in my case, windows do not maximize properly and resize while dragging between screens. I’m probably the last person on earth to learn about this but the primary display can be selected by dragging the top panel to the other screen under Settings -> Display. I still consider myself a KDE guy, but I’m enjoying GNOME a lot more now that I’ve set the larger screen to primary. I should probably RTFM once in a while.