Q:

What is considered room temperature in Celsius?

Recently, I have seen room temperature listed at 20 °C and 25 °C. Which one is more accurate for use in chemistry problems? 

A:

Considering you've read Wikipedia article on room temperature (r.t.), you probably already have an idea that there is no uniformly defined value due to the subjective matter the term is defined upon.
There are numerous standards across industries defining temperature ranges, most of which lead to the value for r.t. of $\pu{(20 ± 5) °C}.$
In natural sciences there are several well-defined standard conditions describing the combination of exact values for temperature, pressure and humidity.
Room temperature is not among these, so ideally, an exact value must be specified alongside, if relevant, e.g. "the parameter has been determined at r.t. $(\pu{20 °C})$".
German Wikipedia article presents an observation that in physical chemistry and statistical physics in European region the typical value taken for r.t. is $\pu{20 °C},$ whereas in U.S.A. the majority of textbooks refer to r.t. as to $\pu{25 °C}.$
In nuclear chemistry, thermal neutron energy $E_0 = \pu{25.26 meV}$ is fixed as characteristic energy at r.t., which is a reference point for tabulated parameters such as neutron cross section.
Using $E = k_\mathrm{B}T$ relation, an exact value for r.t. can be determined, which is usually taken as $\pu{20.43 °C}$ (see e.g. [1, p.  11-173] and references therein).
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, 97th ed.; Taylor & Francis Group (CRC Press): Boca Raton, FL, 2016. ISBN 978-1-4987-5429-3.

