What differs free and paid Personal Diary applications on iPhone 3GS

Hello Techyv.com!
I was actually planning to list all my account usernames and passwords on my iPhone 3GS, I'm sort of having difficulties remembering things especially account passwords. Now I was thinking if a free Personal Diary on iPhone 3GS would be good enough to secure my stuffs, in case I lose my phone. I was also thinking if those paid personal diaries are worth the pay to secure my stuffs. What differs them then? Thank you
