It's actually hard to say what is considered the best mortgage rate possible. This is because everyone generally needs different things and when something satisfies their need, that's the best for them.
Firstly, there are many different types of mortgage plans but there are just 2 types of mortgage rates. They are a) Fixed Mortgage Rate (FMR) and b) Adjustable Mortgage Rate (ARM). As the names suggest, for the FMR, the interest rate will be fixed for the entire duration of the loan but for the ARM, the interest rate adjusts itself after short intervals of time. In order to first decide which is the best mortgage rate for your loan, you need to first decide which type of mortgage rate (fixed or adjustable) is more suitable.
Generally a fixed mortgage rate is recommended for people who plan to live in the house for a long period of time (20-30 years). If you fit into this category then the best mortgage rate for you would be the Fixed Mortgage Rate plan with the best interest rate. But if you only plan to be a homeowner for a short period of time (anywhere between 5-7 years) then the best mortgage rate for your case would be the adjustable type. Here you will need to compare the adjustable mortgage rates (for similar terms and conditions) offered by various mortgage lenders in order to determine the best mortgage rate of adjustable nature.
However if you're not the type of person to take risks, the Fixed Mortgage Rate plan will probably be best for you. It's safer than the Adjustable Mortgage Rate plan because with the ARM, there's a chance that the interest rate can go down, or up. If it goes down then you've made a great investment, but if it goes up then you might find yourself short for cash.
Basically as we mentioned right form the start, what a mortgage lender claims to be the best mortgage rate might not always be the best. It may be the best that he can offer, but the best mortgage rate for your, needs to be based on your needs and preferences. Once you've worked that you should have an easier time getting an ideal mortgage rate for your home loan.