I've been using a Freight Baggage backpack (medium) for almost a year now. It has become my main bag because it is much larger than the Flight. When I do use the Flight, it is obvious that the ergonomics and ventilation are much better than any of my other backpacks or messenger bags. I also like the fact that is fully waterproof, unlike most messenger bag and backpacks. All Ortlieb backpacks utilize a roll top closure or the Tizip zippers found on the Flight. I love these zippers! They are truly waterproof. The top of the suspension frame may hit your helmet, but it depends largely on how you ride. If you have drops that are well below the level of your seat, and you frequently ride in them, it will probably be a consistent problem. I notice it when I'm riding, and I get in the drops. If you do order this backpack, I recommend ordering from a local store or an online store with a good return policy, in case it doesn't work well for you.

There are a few alternatives. Deuter makes a bag, the Transalpine 30 AC, that uses a similar suspension system, called Aircomfort, as the Ortlieb (I think Deuter leases it's designs to Ortlieb). It is not waterproof, but it comes with a rain cover, and it has a slightly larger capacity. It also has the advantage of being the cheapest one out of the three. Deuter makes the same bag without a suspension frame (no AC on the end of the name). Instead it has ventilated mesh stripes, called Airtstripes, on the back of the bag, which I've heard work quite well. I don't like the idea of using a rain cover when the weather gets nasty, but the Transalpine line gets consistently good reviews.

Ergon makes a backpack, the BC3, that is roughly the same capacity, waterproof, and it also has a suspension system (it is completely different though). The BC3 looks very interesting, and the the bag is sold with different sized frames depending on the size and gender of the rider. It may work better for you than the one size fits all suspension frame found on the Ortlieb and Deuter backpacks.