An LOR dilemma... need advice.

[moderatedbliss]

I am a Sociology/Comparative World Literature double major. I intend on applying for graduate schools in Comp Lit. Most of the schools I'm applying for require only two Letters of recommendation.

One of the LOR's will be from the professor who is advising my honors thesis, the thesis is for Sociology but I figure she knows my work and research skills well and can point to specific things.

Here's where it gets sticky:

I've only been in the comp lit major since the beginning of this (senior) year, I'm pretty much doing all of the major in my last two semesters. 
Should I ask a comp lit lecturer I had last semester, or a professor that I have this semester?
The lecturer knows me more as a student and as a human being, but the professor more often writes LOR's and she also is more "reputable" as absurd as that is.. I know that letters of rec from people higher up in the department are preferable.  

I hope I've asked a clear question.
Essentially, between a lecturer (with an MA) that knows me well, or a professor with more prestige that is probably more technically skilled at writing letters of rec because she does it more. 
I don't know if this matters, but I'm applying for progs in the UK.

Any feedback at all is appreciated! Thank you.