Larger employers generally pay more than smaller ones. Generally speaking, BS chemists receive higher salaries if their degrees are from schools that grant doctoral degrees, if they have completed ACS-approved programs, or if they had a high grade point average in their major. Be clear whether this is an exempt or a non-exempt position. Make sure you understand the trade-offs. Starting salaries differ, but the prospect of being paid for overtime may be alluring, but salary growth differs significantly throughout entire career.
Many benefits are negotiable.
For contract employment especially, benefit packages vary. It is the responsibility of the Human Resources group at the firm that made you the offer to help you explore these issues. It is also more difficult to evaluate. Personalities may be a factor, but what your supervisor can and will do for you are far more important. Each job is different, and you probably have an ideal preference.