Just to muddy the waters a bit

In response to your question, I took a look at the LCB and a cordura Imago side by side...I put a 10 inch netbook in a third party thin case, a Nintendo DS in a padded, zipped case, a regular sized 8.5 x 11 notebook, and a Kindle Fire in the padded TB Fire case, and a small wallet in both of the bags. Both of them will handle this load with no problem. I know the stats for the LCB show it as slightly smaller in capacity than the Imago, but they visually appeared fairly equal. As others have suggested, it appears to be primarily an issue of preference: horizontal vs vertical. That being said, for me personally, these items felt more secure in the LCB- probably because the opening isn't quite as wide due to the vertical nature of the bag. Also, the LCB gives you a little more flexibility because of the lack of internal pockets so it felt like a could kinda squeeze more things, adjust how they are within the bag, to fit more. And the LCB can have the absolute strap as well
It sounds like you already know you want a messenger bag, but just have to ask, have you looked at the Synapse? I'm not a backpacky type of gal- the Synapse is my very first one!- but it is freaking awesome and can hold your load plus way more while not looking like you're carrying much at all!
But back to the LCB and Imago...All that being said, I don't think you can go wrong with either bag. They're both awesome bags. If the ol' credit card can swing it, you might consider ordering both and loading 'em up and see what your preference is and returning the other (of course then you run the risk of...wanting both! LOL!). Good luck! I don't think you can go wrong with either bag!