Letter of Recommendation: Reputation vs personal relation I want to apply for a graduate program in Computer Science and need a Letter of Recommendation to complete my application. 

While thinking about who I could ask to write the letter I came up with two people: One is a full professor and has a lot of reputation but knows me only from some oral exams (where we had some good talks even beside the exam topics) and crowded lectures where he couldn't really take notice of me.

The other one holds a Ph.D. in CS but is no longer involved in research. However, he holds advanced lectures in the field I'm interested (and am applying for). Usually we are about ten persons in his lectures and he knows me very well from asking questions during the lecture and so on. When he's asking a question to the audience and I raise my hand, he usually says that he knows I know it and wants others to answer it. 

I'm unsure if I should aks the full professor with a lot of reputation or the lecturer who knows me much better but has much less reputation, to write a letter for me.
The more a person knows of you, the more positive things they will have at their disposal to write about. As you explain it, your second option knows about your skills and probably could redact a great recommendation letter.

That being said, I do not think that it hurts to ask both. If both agree, you can submit both letters