I have not been on either but around the Beneteau Oceanis line from 37 thru 50 a lot including the 43 I have now.
I looked really hard at the Jeanneau 409 when it was introduced. The 439 which was on my short list trailed it by almost 6+ months in some areas in USA. The hull shape and several bells/whistles on Jeanneau are really nice i.e.; main sheet routing.
Just saw a new Beneteau Oceanis 50 at the Strictly Sail Pacific show and they have copied the chine ( some other things) which is also used on the Sense line.
Also went on the Jeanneau 509 - VERY nice.......especially down below which a couple of hard core racers thought was too "foo-foo" but I thought it was stylish yet functional.
What is most important to You? Performance, Comfort, other(s)?
How do You plan to Use the boat? weekends, racing, long distance cruising?
Best advice = Spend time on both.....lots of time. Walk the docks & see if You can talk to some owners & get aboard. More than a few dealers will take prospective buyers out for test sails. But the most important part, is to go back the 2nd & 3rd time because You will get past "emotional" reactions, see things you did not see the other times.
Charter them first if possible - With this much $$$ at stake, you do not want to have any regrets
Good Luck with a fun pursuit
P.S. Just noticed your DC location - lucky You = Both Mfg are well represented in Annapolis - You can get rides with no problem + find owners to talk to........do You plan to sail in that area?
Also here's link to Beneteau & Jeanneau owner's sites