As some industries consolidate many major players in related industries shift from using the default provider to smaller providers, and it makes sense that they do because there are a boatload of benefits

• A smaller business will get a brand and credibility boost by having a client list that includes other well trusted well known brands. They may be willing to sell cheaper due to gains in productivity brought on by increased volume and other secondary sales brought on by the brand boost.
• Since the business is smaller your account will be a larger percentage of their total business, and their customer service will likely be better.
• If you go with the industry leader you may help drive competing businesses out of the market. When a near monopoly exists the lead company can increase their prices and eat into your margins.

I never went to any business school, so this may be hosed and idealistic or otherwise a bunch of crap. Feel free to let me know if it is :)