Compound having highest standard reduction potential
Top 5 oxidants from the CRC Handbook of Chemistry and Physics [1, p. 5-83]:

TABLE 2. Reduction Reactions Having $E^\circ$ Values More Positive Than That of the Standard Hydrogen Electrode
$$
\begin{array}{ll}
\hline
\text{Reaction} &amp; E^\circ/\pu{V}\\
\hline
\ce{F2 + 2 H+ + 2 e- ⇌ 2 HF} &amp; 3.053\\
\ce{Tb^4+ + e- ⇌ Tb^3+} &amp; 3.1\\
\ce{Pr^4+ + e- ⇌ Pr^3+} &amp; 3.2\\
\ce{Cf^4+ + e- ⇌ Cf^3+} &amp; 3.3\\
\ce{XeF + e- ⇌ Xe + F-} &amp; 3.4\\
\end{array}
$$

Note that standard reduction potential is not characteristic for a single compound. Instead, it is only makes sense for a given redox pair – of course, assuming standard conditions ($\pu{298.15 K}$, $\ce{101.325 kPa}$), activity of all soluble species $\pu{1 .000 mol L-1}$ and measured against the standard hydrogen electrode.
For example, iodate $\ce{IO3-}$ has very rich redox chemistry and many SRP values [1, p. 5-79]:

$$
\begin{array}{ll}
\hline
\text{Reaction} &amp; E^\circ/\pu{V}\\
\hline
\ce{2 IO3– + 12 H+ + 10 e- ⇌ I2 + 6 H2O} &amp;1.195\\
\ce{IO3– + 6 H+ + 6 e- ⇌ I– + 3 H2O} &amp;1.085\\
\ce{IO3– + 2 H2O + 4 e- ⇌ IO– + 4 OH–} &amp;0.15\\
\ce{IO3– + 3 H2O + 6 e- ⇌ IO– + 6 OH–}&amp; 0.26\\
\end{array}
$$

References

Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data.; 2017; Vol. 97. ISBN 978-1-4987-5429-3.