I am leaving my job soon and am looking for letters of recommendation. My problem is, I've worked more closely with my customers than my project lead (not technical) or manager (the customers usually talk to me first and rarely even if CC my lead if I don't). So in this case, the customer has seen my work more closely than my leadership and can better attest to my abilities, communication skills, and performance.

Are recommendations from customers viable, or will they be largely dismissed? Secondarily, can they be more useful than letters from managers that don't really know your work at all?

Note: I already have a letter from the only coworker I've really worked with, but I'm looking to get more than one for good measure.