FREA, The Foundation of Real Estate Appraisers. They have some great packages if you also sign up for their public record data (includes plat maps, and flood info, and great search tools). They also offer reduced rates on CE credits, group health benefits for independent/fee appraisers Talk to J.D. Peterson 858-483-2490 to see if they cover your area, or www.frea.com. Use your appraising smarts, get good comparables and make an informed decision and see who gives you the best value.
It depends on who offers coverage in your state. Each state varies as to who writes (losses, regulations, etc.) so while X company may offer the best rates, they may not offer coverage where you are. Just do your research and good luck.
I use our state's mandatory insurance company since I am a real estate broker. The cost is minimal...$100 for an appraiser's endorsement. If I had to choose...Liability Administrators. They have come in and put on seminars for our local appraiser's group. I was impressed.