Most people find 45's more comfortable to shoot than 40's; slow push vs. quick slap. However 45's in small guns are always a handfull.
I'm not a big fan of DA pistols, reguardless of mfgr. After watching and range officering for people whooting DA's I've noticed that even the best shooters will send their first shot low, their second shot high, then start making good hits.
Bottom line, a newbie does not need the distraction of trying to learn two trigger pulls at the same time, and an expeirenced shooter, however well he does with a DA, could do as well or better with a SA or DAO.
Although I understand some people like a gun with a lot of "modes" and buttons and levers cause guns like that seem like you're getting more for your money and you get to do fussing and cocking and decocking.