User Registration solution pack is a prebuilt solution, so if your data doesn't match the ones stored in the database created for the solution, it will require more work to modify to work with your site. It is simple to implement if no modifications are required.
SecurityAssist allows you to customize your pages more easily, but you will have to know a little more about what you are doing.
What are the different information that you are storing in the database (username, password, usertype, etc)? If its close to what is stored in the database for the solution it might be easier to use the solution pack. If you let me know I can point you in the right direction.