I was wondering if anyone has any thoughts on which makes a better container for an aviation survival kit, a Pelican type case or a backpack or some similar soft type case? Each seem to have their pros and cons but my main concern is the ability to get it out of the airplane ASAP in the event of a ditching or forced landing. Any ideas?

well i would go for the backpack:
-cheaper than large pelican case ( not always, though )
-easy to grab
-easy to carry

to add the waterproofness / ability to folat of a pelicancase, just use a heavy duty waterproofliner. ( a thick survivalbag can be used like this too and has more uses ) Protectiveness to your more fragiale gear, can be done by rolling in to, clothing, blanket, sleepingbag, etc. If it need more protection, than put it in to a small container , before you roll it in to something.

Paula,
I don't fly so I don't know what your needs are, but I know that there are dry bags made for river rafting that have straps like a backpack, but are waterproof. They are heavy, but may be a nice compromise.
Biscuits

I'd tend to agree with PC2K, the pack (with it's packstraps, grab handle, gear loops, etc) would be easier to hold on to, and there's something to be said for the ability to wear it on your back once you're out of the plane, leaving your hands empty and free while you're moving. Waterproof bags inside a pack also give you a surprising amount of bouyancy if you end up "in the drink" (see any field manual for ALICE gear ruck and liners or try it yourself). Regardless of how tight you pack the waterproof bags/liners, unless you vacuum pack them, there's still a lot of air space inside of them, a 60 Lb ruck will float itself and have plenty of flotation left to share with you.
Just my two cents.

Troy

how about a waterproof deckbag inside the backpack

I think Doug's article on equipping Simon T for an air race is an excellent read, even for non-pilots like myself. The key to ensuring you have the proper survival gear with you in a fast, emergency egress is to wear it. Doug configured Simon's gear to fit in his flight suit and vest, both of which are hopefully leaving the vehicle with him! <img src="images/graemlins/grin.gif" alt="" /> If you are not wearing a flight suit or not flying over water, then wear pants with cargo pockets and hunting or fishing vest to stash your gear. Larger gear can go in a separate bag or container that you grab hold of on exiting the plane, but redundent PSK type of gear on your body helps ensure you have what you need to survive.

BTW, one comment on using a backpack. I use a backpack to lug my laptop and other stuff when I commute. The straps tend to get hung up on thinks (gear shift, etc.). I would imaging you'd want to secure the straps for use in a plane, otherwise it may get stuck and you'd have to make a quick decision to spend time unsnarling it or to leave it.