I've been using mSecure for about 4 months and I love it. I downloaded 1Password and 1Password Pro a few weeks ago when they were free, but haven't gotten around to playing with them yet.
I see that 1Password has the ability to autofill webpages, where mSecure doesn't. That's cool, but that's not a feature I needed (plus, i don't think they had that feature when I was in the market for the app). So when I was ready to take the plunge, I decided to save money and spend $3 on mSecure instead of $5 for 1Passord or $8 for 1Password Pro, and haven't regretted it a bit.