A growing national business with $12M + annual cash flows (still technically a small business, so probably not relevant). We worked through small local midwest

A growing national business with $12M + annual cash flows (still technically a small business, so probably not relevant). We worked through small local midwestern banks, but found the larger banks (e.g. Wells Fargo) and American Express were necessary to get required US services (credit lines, commercial paper, credit card expense reporting etc). American Express has been a pleasant surprise as much of our cost of doing business is paid that way, for which we get (valuable) points/perks. Something I think not enough businesses use. Larger banks also seem to make it easier to remove personal guarantees on credit facilities as tbe company grows. As for how much to allocate to each account, most banks provide a sweep service if balances are large enough where the balance of each account is sweeped nightly into a money market account, and then restored the next day, Otherwise you just need to maintain balances in each bank account in support of your cash flow projections. As for international finance, I have found that foreign banks (e.g. ANZ Banking Group, Royal Bank of Canada) are much better with transfers and moving money around than US banks (as they are not stymied by the Federal Reserve and the Fed Payments System). Do not overlook Bitcoin either. Where small local banks shine for us is through their trust departments. Larger banks tend to have trust products and packages for "wealth management" into which funds are dubiously recruited, while with small trust companies, you can engineer boutique situations (e.g. where fiscal instruments such as securities and time deposits can be held as collateral but still traded on the open market under a trust account). Befriend a small bank trust officer! Transfer of large amounts of money between banks in the US is still very much a credit transaction - availability of funds are determined by the credit of the parties to the transaction. New companies with large transfers even between large banks will get restricted funds availability, until credit develops. Working with larger banks, it is much easier to establish funds availability in conjunction with a more holistic credit picture. I'm sure for legitimately large corporations, there is a need to diversify among the top 13 banks, especially for national businesses (e.g. not even Wells Fargo is in Missouri or Oklahoma). We have found there effectively are NO national banks in the USA present in all states (we have personnel in all the lower 48). As in politics - when you're small you are either Democratic or Republican. When your large it is necessary to contribute equally to both. I think the same is true of banks - a business of $100M or more would want to diversify even if just for risk management. I agree with @davismwfl that you need to construct a banking relationship around your systems.