I use a Tenba DNA 15 Messenger bag. Yes, it's a camera bag (and I originally bought it for that purpose), but the camera padding insert comes out and it becomes a regular messenger bag. It has a laptop slot and a smaller tablet slot built into the bag, and lots of room to fit multiple other devices. It has all the features you want such as the handle attachment, and many pockets. I use one as my daily bag, and it has replaced my backpack. It fits as much as a large backpack, yet it will fit under the seat on aircraft, and is personal item sized.
If you want something smaller, the DNA 15 also comes in a slim version which is less bulky and less tall. If you want something even smaller that can still fit two laptops, the bag comes in sizes 8, 10, 11, 12, and 13 (which correspond to the measurement of the bag similar to how laptops are measured)