請教：resume format for contract work

以前曾經work on contract for 6 month on site  in a 500 fortune company A, while hired by a small placement company B.  How to write in resume. Here are two formats: 

1.  Company B
IT consultant on site  in Company A
.....responsibility and achievement 

2. Company A
IT consultant
......responsibility and achivemenet

I used to write in format #1. Now think that I should do #2 format. What are your suggestions?
Thanks.