The main difference between banks and brokers:
1)Brokers have all the rates with all the bank, non-bank lenders they are associated with. Bank can provide the rate with their owner programs.
2)Brokers can get wholesale rate; lenders has rental rates. Not necessary wholesale rate is better than retail.
3)Banks can handle certain scenarios better. Like, stated-income self-employed loans; low down payment loans. They don't have to follow Fannie Mae guideline if they decide to keep your own and your loan is a special case. For brokers, the loan has to be "saleable".
4)I won't see which rate is better. You need to compare.