Some will say at both times! Yet, conventionally we consider ovulation the most fertile time. There is probably very few women who actually ovulate on day 14 and if you would like to maximise your chances of conceiving, I'd consider temping and charting to get a good feel for your cycle. You can then start making an educated guess at your most fertile time.
Good luck with it. We're currently trying to conceive only I am using cervical mucous and symptoms as being my third, I'm a little more attune now. First two I charted, temped and used OPK's. It helped to understand my body alot. :)