They both have their advantages. I will list 4 major advantages of each, there may be more but this is the short version.
It is important to know when programming how to prevent hacking. Here is another way where PHPixie works great and as expected.It appears to me that PHPixie protects against alot of stanard hacking if used in the proper and expected way:
When getting post data, instead of using the standard PHP: $_POST["variable_name"]; (WRONG)