The global company that I worked for recently was required of having multiple vendors by its ISO 9000 quality system. The rationale was that if one of them was unable to provide the necessary goods and/or services, there was a fallback. However, the downside of that reasoning is that if you divide your purchases between two or more vendors, the impact of your business on any one of them is less. This is particularly true for small businesses.
Giving increased business to a vendor with the expectation of improved service from them only works well if you have a personal relationship with the vendor. When working for a much smaller company, I always tried to match the vendor size to our size. Too large and we were less likely to command their attention. Too small and there was a distinct possibility that when the chips were down, they would fail to meet commitments. This mostly applied to custom goods and services.
Off the shelf items were usually purchased from a single supplier but could be purchased from any qualified vendor. In the global company, this would not have any particular significance since the the annual purchases ran into the millions of $. For the small company, we were so much smaller than the vendors we were using that our purchasing level was of little consequence. The exception was when we were working with the traveling sales reps. They were hungry enough that they appreciated the business that we passed their way.
From an accounting point of view, fewer would be better. The bean counters at the global company used to tell us that it cost over $500 to qualify a new vendor and they strongly resisted doing so. It usually took an approval from one or two levels above to use an unqualified vendor. Hopefully, a smaller company doesn't have that kind of bureaucratic overhead but it still detracts from the paying work.
I would go with what ever he wants.