Both mph and CFM are essential, and neither is more important than the other. Don’t be fooled by a leaf blower with one measurement that’s exceptionally high and another that’s low. You should consider both mph and CFM, not just the highest one.  Here’s why: A leaf vacuum with an unusually high mph coupled with a relatively low CFM may not be the tool you need, despite the impressive mph. Even if the air moves through the tube at a fast rate, it won’t significantly impact the leaves if there is only a small amount of moving air.