First-time Home Buyer:Rates from Bigger Player VS Smaller Players

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Hi,

I am first-time home buyer and currently in the process of getting pre-approved by a well-known big home loan provider. I compared the interest rates and POINTS with the rates of smaller home loan companies.
The difference was astonishing. The smaller companies were often 1.5 or 2% lower than the bigger ones.
I understand that smaller companies have to stay competitive, but why is there such a big difference?
Also how trust-worthy are smaller home loan providers vs the well-known bigger ones?
What should I look for when choosing my home loan provider, besides the obvious interest rate,Points,APR?

I would appreciate your feedback.