After using the blitz containers that I bought last month, my first impressions are that the spout on the aquatainer is much, much better than the one on the blitz. There's no on/off valve on the Blitz, so you can't leave the spout on without risking contamination or spills. Plus you have to really crank down the cap in order to get it to seal without any leaks. There's no vent plug on the Blitz either, I guess the nozzle is designed in such a way as to allow venting. This means the flow isn't as fast as the aquatainers, but for me that probably isn't going to be a problem. I prefer to have less sources for leaking.
Other than those issues, I actually like them a lot. The size is a lot more managable, I think mostly due to the narrower profile that allows you to carry it without it banging into your legs. I can probably carry one in each hand and walk, something I can't do with the aquatainers because of the boxy shape. Also, it takes up a lot less floor space than the aquatainers. This wouldn't be a problem if I was able to stack the aquatainers on top of each other, but that goes against the manufacturers recommendations, and I am pretty sure that would cause it to leak.
For long term storage, I'm probably going to pick up a few more Blitz containers. But for frequent use, like camping, the on/off nozzle on the aquatainers and the ability to lay it on it's side make it much more useful. If I could somehow adapt the nozzle of the aquatainer to the blitz, it'd be the best of both worlds.