CI2.0 or CI1.7.x for new project?

[eluser]CodeIgniterStep.Com[/eluser]
Dear All,

I have developed my project with CI 1.7.x , Now I have a new project and I have upgrade PHP to version 5.2.6 and supported 5.3.x.

Should I use CI 1.7 or CI2.0 for my new project?

Thanks