Does the mRNA model more closely resemble the DNA strand from which it was transcribed or the complementary strand that was not used?

mRNA more closely resembles the strand of DNA that was not transcribed. 

Why: Bases in DNA always make one of two pairs, either C-G or A-T.  So, a strand of DNA coded ATCG would have a complementary strand of TAGC.  

 RNA bonds to DNA in the same manner, except instead of T, it uses U.  So, the DNA strand mentioned earlier, ATCG, would be transcribed into UAGC.