I'm in agreement about stability. Also, depending on how you use your device, i.e. how much data usage you have, the battery life on the BB is better than the WM devices. I go days without charging my BB. I believe I read somewhere that the blackjack comes with two batteries so that the user can make it through the day without plugging it in. Although, it may just be a plot to get the user to reboot the dumb thing rather than tell them that it has to be rebooted constantly. lol.
As for security, there really isn't any to speak of on WM. If you aren't a corporate user, I doubt this would effect you. But I can lock the BB's down so tight they are almost unusable. That's a lot of security options and I like having them despite the fact that I don't employ most of them.