What are chemical candidates for replicator molecule?
There is no accurate answer  , as you say we talk about candidates . there is lots of strong theories about the origin of self replicators . RNA world was a strong candidate since latest experiments that suggest there is a good chance that some molecules that have simpler structure than RNA , could have a chance to do self replications .
    there is also strong theories such as :

1.Prions that delivered by space objectives and Meteorites . 

2.Life's origins may result from low-energy electron reactions in space:

http://phys.org/news/2016-06-life-result-low-energy-electron-reactions.html



first self-replicator recreated in lab:

RNA, or something very like it, has long been a strong candidate as the first self-replicating molecule in the origin of life. This is because it can both catalyse chemical reactions and carry genetic information.
But chemists first needed to explain how a large, complex molecule like RNA could form spontaneously to begin the process. They had done so for some, but not all, components of the RNA molecule.

https://www.newscientist.com/article/2088006-building-blocks-of-lifes-first-self-replicator-recreated-in-lab/

The origin of replicators and reproducers: 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664675/

you can also check the topic :The RNA World and the Origins of Life 
from the book :

Molecular biology of the cell by Alberts B, Johnson A, Lewis J, et al.  



after all this article was so innovative for me . I think it's a good explanation for self replication of molecules simpler than RNA.

http://www.nanowerk.com/nanotechnology-news/newsid=40896.php

"Maslov and Tkachenko's model imagines some kind of regular cycle in which conditions change in a predictable fashion—say, the transition between night and day. Imagine a world in which complex polymers break apart during the day, then repair themselves at night. The presence of a template strand means that the polymer reassembles itself precisely as it was the night before. That self-replication process means the polymer can transmit information about itself from one generation to the next. That ability to pass information along is a fundamental property of life"