You may have a specific interest or a particular dislike for certain industries.
Some firms deal heavily in non-profits, government, health care, etc.
Knowing your strengths will help you use this information to distinguish between the various firms. Obviously this number will vary widely with the size of the firm, ranging from less than a dozen to hundreds. However, once you know the number of partners and the staff size, a bit of quick mental arithmetic will give you the ratio of staff to partners, and this is very important information. Consequently, you may be comfortable with either situation, but you should know the facts from the start. The answers here will tell you the amount and rate of growth of the firm.