I am applying for a Ph.D. position in US universities. I am confused about whom should I use as one of my recommenders? One of them is from the school from which I graduated and he is the department head, had been a postdoc in one of the US's top universities. I took one of his courses and he was my course advisor at that time. On the other hand, another one had been my supervisor for two projects (in my workplace) and is very young (doing his first or second postdoc). We did not publish any articles yet but they are under review. So basically she can write better about my research experience and so on. I am confused because I attended a webinar from a US school lately where the department head said they prefer LORs from someone who had been my supervisor or knows me via research, not someone who knows me via one or two courses. Whom should I choose as one of my recommenders?