What a provider actually is
Meta does not sell WhatsApp Business API to most of the small and mid sized businesses, but acts as the platform between the company and the Business Solution Provider, or the BSP in short. The solution provider handles billing, the dashboard the company will be using, the automations, and the day to day support. In other words, it is choosing who will be handling those aspects of WhatsApp business account management.
Questions worth asking before you sign up
A few questions tend to distinguish between a good and a bad provider. Some examples are: will the support be on a personal level or will all of the communications be funnelled into a general address where you will have no idea who actually sees your request, is the pricing clearly stated on the website or will you be pushed to contact someone so that the terms could be decided individually, are you going to plan the automation and chat bot flows together or will you pushed to the dashboard and left to figure the rest out on your own, and will you be able to recover if an account gets restricted. And a few things worth noting are:
Red flags
There are a few red flags that indicate deeper issues. Those are: unclear pricing that is only available upon request rather than being openly visible on the website, lack of clarity about who handles the technical part and what the technical part actually is, and general support that is funnelled through ticketing systems rather than having a person who handles your account and knows about it. A provider who lacks those three tend to either leave you to figure out the automation flows on your own (despite offering BSP services) or hide the additional costs that are only visible once you get into the specifics of an individual account opening.
Why this decision matters more than you think
It requires an additional step to sign up with a new provider, and depending on the circumstances could require additional charges. And in some cases, especially if the account history and message history are involved, could diminish the general quality of an account. A number that had to be recovered after being placed on restriction will have trouble getting to higher messaging tiers even if the message quality is good, since it takes time to recover the reputation of a number that has been through such a process. It is better to avoid the trouble of number recovery by choosing the right provider rather than dealing with restrictions and diminished performance levels months down the line.
And where to go from here
The sort of decision that is better made through direct communication rather than research. Some of the details that define the difference between good and bad are difficult to find on the websites of potential providers.