A fixed rate loan program has the same interest rate for the life of the loan and the monthly payments (principal and interest) never change. If you escrow your property taxes and insurance, those expenses can change, which will affect your monthly payments. Fixed-rate mortgage may be a good choice if you plan to stay in your home for a long time or if you feel more comfortable knowing your payment will not change.
Rates will generally increase when you exceed the local conforming loan limit.