Well I purchased a ; Targus XL Citygear Messenger Notebook Case - for the simple reason that I needed something to stick the laptop in and quick. It's not a bad bag, its not exactly to the standard that I'm used too though I must say.
I was considering purchasing a Belkin Impulse for no other reason than it looks sturdier than the existing Targus bag which seems to get its rigidity from either the laptop or the 'files, folders, magazines' that you're inclined to stick in the bag along with the laptop, its got 3 compartments the 2 outer and 1 inner compartment is where the laptop resides.
The annoying thing for myself is that I managed to pick up a bargain bag some years ago that I used to haul my previous workhorse of a laptop a Dell 15.4" around in. It only cost something like a tenner and was an absolute steal at that price, made by Belkin who incidentally don't seem to have any record of the case itself. It seems they just purchase 'job lots' of things sometimes and stick their name to them then sell them at a reasonable price. So I've no possibility of finding another bag like that at such a good price, I know, I've asked, emailed and looked.
The closest I've got is a Wenger WA-7653-14 Legacy Triple case 17" black which I must say has all the features of the previous 'Belkin' model. Most notably its sturdy on its own, it doesn't need rigidity provided by what its carrying. It has the facility which has always been important to me to be able to insert the laptop inside, then you unzip it to reveal the 'workstation', you can then have it on your knee safe in the knowledge that its not going to flop down on you, you can use the laptop and its well cocooned and protected. I also liked the little Velcro strap inside which held the laptop tight, but also the Velcro separator which permits you to carry the power adaptor without it impacting upon the laptop ie: scratching it at all. That said its waterproof like no other, but also its heavy so if you're likely to be travelling far, it may not be the most ideal bag without the aid of a trolley, of which the original Belkin allowed. The Wenger doesn't have a back view so its impossible to say whether it's includes.
I have to say however, that Choroka K1 looks like a nice bag, no 'top handle' however, which would bug me. That said its especially roomy. However, in this day and age I would be more likely to go for a backpack if I was expected to carry it around say between buildings, I would ensure it was waterproof - there seems some question as to the Choroka's ability on that score. I would use a backpack for security, afterall its impossible for someone to 'grab' it off you when you've got both arms through the hoops, handy if you ride a bike, or to load carry when walking keeping your hands free. An altogether much better option in my informed opinion something like a Wenger or Swissgear.
HTH