Your best financing terms and rates will be either FHA or 30 year fixed conventional through Fannie/Freddie.
As @Brian Garrett mentioned Fannie Mae will be your best rates on 1-4 units. FHA is only an option for an owner occupied 1-4 unit property. If you are talking about large multi of 5 units or more and a million dollar loan amount or more, then your best bet is a mortgage banker / broker that does Freddie Mac or Fannie Mae small balance commercial or multi financing. You can get low fixed rates for 20-30 years terms and it will be non-recourse.
If the loan amount for the 5 units and more will be less than 1 million then your local credit union would be the 1st stop I would make, followed closely by local community banks.
Are you targeting turn-key properties or will they require rehab?
@Farris If you want to grow faster and recycle your down payment funds from project to project, I suggest acquiring foreclosed properties, rehabbing and renting out. You can use portfolio lending to refinance every 90 days or so and cash out original down payment funds to use toward the next project. I've been using this strategy for years.