Answer
5.5$\%$ compounded semiannually
Work Step by Step
After $t$ years, the balance, $A$, in an account with
principal $P$ and annual interest rate $r$ (in decimal form)
for $n$ compoundings per year: $\displaystyle \quad A=P(1+\frac{r}{n})^{nt}$
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For $5.5\%,$ compounded semiannually (n=2):
$A=5000(1+\displaystyle \frac{0.055}{2})^{2\cdot5}\approx 6558.26$
5.25$\%$ compounded monthly (n=12):
$A=5000(1+\displaystyle \frac{0.0525}{12})^{12\cdot 5}\approx 6497.16$
Return is greater for for
5.5$\%$ compounded semiannually
