A verdict based simply on the comparison of stories improperly shifts the burden of proof to the accused and does not respect the principle of reasonable doubt.

An accused’s evidence cannot be rejected simply because the evidence of a complainant is accepted. W.(D.) precludes this “either/or” approach to the assessment of credibility. More is required.

R. v. W.(D.), 1991 CanLII 93 (SCC), [1991] 1 S.C.R. 742: the W.(D.) test requires that judges and juries refrain from engaging in “credibility contests” between the accused and the complainant.
Wherean accused testifies and isn’t impeached, there is a route to conviction, however.  A trial judge can reject the accused’s evidence based on compelling conflicting evidence, the truth of which the trial judge accepts beyond a reasonable doubt. 
This was explained by Justice Doherty in R. v. J.J.R.D. (2006), 2006 CanLII 40088 (ON CA), 215 C.C.C. (3d) 252 (Ont. C.A.). He wrote: 

An outright rejection of an accused’s evidence based on a considered and reasoned acceptance beyond a reasonable doubt of the truth of conflicting credible evidence is as much an explanation for the rejection of an accused’s evidence as is a rejection based on a problem identified with the way the accused testified or the substance of the accused’s evidence.
The “reasoned acceptance of a complainant’s evidence” that would justify the rejection of the evidence of an accused must occur in the context of a proper consideration of the whole of the evidence.
R. v. Wills, 2016 ONCA 965 (CanLII), at para. 15, rejecting the Crown’ argument that the trial judge’s reasoned acceptance of the complainants’ evidence justified his rejection of the appellant’s evidence.