I use a Pelican 1700 as it is not over-sized. I also got the replacement foam pack and so I have three extra foam templates, depending on which guns I bring.
As for flying with firearms, your case just has to be hard sided and has to lock. A few notes about that:
1) Hard sided is intended to protect your guns. I would really recommend spending the money on a good Pelican case (or similar) and not a cheap plastic case. The abuse my Pelican gets isn't pretty.
2) Your case should have two locks so someone can't pry the case open. The locks MUST be heavy locks, I use they keyed brass Master padlocks (you can get them at Target or WalMart.) You can NOT use TSA locks on firearms (unless you don't want to see your gun again.) The TSA will have you lock it, you keep the key, and if there is any question, they will just get a hold of the airline to contact you.
3) "Oversize" means more than 62 linear inches, length x width x height. As an example, the Pelican 1700 is under that, the 1720 is not. The oversize baggage fee is $100 to $200, PER BAG, EACH WAY.
I travel one to two times per month with firearms, and when I do, it is really no issue to check them. You go about 1/2 hour early, check in, and declare your firearm. They airline agent will have you sign an unloaded firearms declaration card (ammo can be in the case, just not the gun). Then the agent will do one of three things:
1) Take your bag, put it on the belt, and send you to your gate (I live in Baltimore, and this is what they do at BWI.)
2) Take your bag and ask you to stick around for 15 to 20 minutes in case TSA has any questions (they did this in Monterey to me.)
3) Call for a TSA agent and have you wait, or take it to the TSA screening station. This happens to me at LAX and can take up to 1/2 hour for the TSA agent to come when they are busy.