Who should I ask for my third LOR? (Clinical/school psychology)

[transfatfree]

Hi all,

I'm an international student planning to apply for clinical psychology (and school psychology) programs in the US. As I was not a psych major I completed an MA in psychology. So far I've ask a clinical psych professor (I helped at his lab for more than a year) and a cognitive psych professor (she was my thesis supervisor) to write LORs for me. I've read guide books and posts but still can't make up my mind with the third one. I hope you can give some opinions about which one would give me a better edge:

1. a senior lecturer from the UK (non-psych but he was the supervisor of my non-psych master's dissertation. Last contact was 5 years ago but pretty sure he remembers me as I was one of his first students.)
2. an associate professor from my home country (she's an educational psychologist and I got an A for her class for my education diploma. She also wrote me an LOR for my application for my MA in psych. Last contact was 2 years ago. )
3. an associate professor from my MA in psych (he's a developmental psychologist and I got an A- for his class.)

Any thoughts are welcome!