The Service Provider License Agreement (SPLA) is much more flexible than the ISV program. It allows you to license MS products on a monthly subscription basis, during a 3-year term, while enabling your organization to use the products to provide software services to customers.
The following scenarios would make the SPLA program the best suited for you:
Some of these scenarios will qualify you for both the ISV and SPLA programs, therefore you will need to look at each licensing program and choose which will benefit your individual business needs the most.