Your best option is to get the credit score up higher, because you are going to pay a lot more for having credit scores that low.
You should check to see if you are eligible for a HARP refinance http://(www.makinghomeaffordable.gov
). If so, you can get a decent rate with limited or no PMI, depending on your current loan.
If you are not eligible then you can look at either conventional financing or FHA. FHA will be a lower interest rate, but you will probably need a 640 credit score and the PMI is very high. If you go conventional, then you'd probably be looking at paying points AND having an interest rate in the 4.5%-5% range.
In my opinion you would be best served by working on the credit first and then applying for a refinance. It could save you thousands of dollars in charges.
If you would like to discuss things in further detail and get some pointers then please feel free to shoot me an email or give me a call at 866-936-5363 ext 278