I have an account at each.  I have a checking account with a big bank, and another savings account with a credit union.  (My grandparents taught me a long time ago to diversify, and not do all my banking at one place...)

The reason I got the checking account was that it was literally free checking and all my ATM usage fees are reimbursed to me.  I also got a VISA debit card, that my credit union was unwilling to offer.  It's a real convenience for a single, working parent.

If my credit union could do all that I'd have my checking account there in an instant.  As it is, if my balance falls below a certain amount every month which it occasionally does in a tight month I get charged a fee.

Bummer.  

I'm sure that there are credit unions out there that don't do that, but none that I have found in my area so far.