which one is easier?
which one is more useful?
which one is a better choice for molec bio and genetic?

It is recommended by the department that you take both. I'm taking 2D03 this year and will probably take 2F03 next year. Not sure how they relate to molecular biology and genetics, but it's probably just a general course and later we'll be moving more into the specifics.

I took both last year. In terms of difficulty, I found them both to be easy. 2D03 has labs, while 2F03 had just lectures and tutorials. To be honest I never went to lecture for 2F03 because all the notes you needed to know for the midterm and the exam were always posted.
In terms of usefulness, I would say 2D03 because of the lab component so I guess it would be a better choice?
hope this helps a little.