Both the UD-60 and Tenba Small Messenger are fairly large size and roughly the same dimensions. I have looked at both and liked them both, but I bought the UD-60. The top opening is the big difference to me and I am still not sure which I prefer.
The UD-60 has a zipper-slot opening which is easy to work out of, but more difficult to initially get the camera/lens combo through. The Tenba has a flip-top which makes getting the camera/lens into and out-of easier, but seems to get in the way when I am using it (i.e. switching lenses). The UD-60 seemed a bit slimmer when loaded, but they are both pretty large. I can easily carry 2 cameras mounted with lenses in the UD-60 plus an additional lens or two and a flash.
I do like the Tenba insert (used in the messenger) and have two of them which I use in non-camera bags. I find the size of that insert perfect for my 3 lens zoom (large) with camera outings. Since I like it separately, I would probably like the Tenba bag which uses it also.
I only carry a 13" thin Apple laptop, and it fits with room to the side for the card reader, charger and cables without having to put them in the bag pockets thus keeping the slim profile for the bag. A 15" laptop would not be able to do that.
Hope that helps a bit ...
-howard