I have a general question regarding documentation and petition preparing for H1B

I work in a popular Indian IT company. When we travel in H1B my employer's US branch is my client and the actual client for whom we develop application is our "end client". This is what we tell in our visa interview. Therefore when we prepare documentation we can provide our work location as either US branch's address or end client's address. Now the catch is

a. If we provide end client's address as work location then we need client letter and produce that in the visa interview
b. If we provide my employer's US branch address then I don't need any client letter

1. My question is which option is more safer from petition approval and interview perspective? If I show end client address as work location and produce a client letter then does it makes my case stronger or it really doesn't matter?

2. Does the project duration in my petition decides H1B duration? I mean if in my petition I show my project duration is of 12 months then are they going to give me 12 months of visa or regular 3 years of H1B visa? Last year in 2012 I have seen many people getting only 1 year of new H1B visa. Don't know the reason behind that.

3. If I get my visa stamped from my current Indian employer and then change the company and join another popular Indian IT company then can I still travel with the H1B from my new Indian employer for a different client? If yes, then does it matter if I have shown client letter or not in the visa interview from my previous employer? This question may sound stupid but still asking as I clearly want to understand the rules?