I prefer the SQRT symbol with the closing downward tick, and have been using this answer to achieve the desired effect. However, when I hugely increase the font size and use fixcmex to achieve some nicely scaling symbols (required for a nice fix to matplotlib plotting) the SQRT downward tick no longer scales nicely.
Compare
Normal font size
Massive font size (50pt)
MWE
\documentclass{article}
\usepackage{lmodern,amsmath,amssymb,bm,physics,letltxmacro,fixcmex}
% Gives the nice SQRT symbol.
\makeatletter
\let\oldr@@t\r@@t
\def\r@@t#1#2{%
\setbox0=\hbox{$\oldr@@t#1{#2\,}$}\dimen0=\ht0
\advance\dimen0-0.2\ht0
\setbox2=\hbox{\vrule height\ht0 depth -\dimen0}%
{\box0\lower0.4pt\box2}}
\LetLtxMacro{\oldsqrt}{\sqrt}
\renewcommand*{\sqrt}[2][\ ]{\oldsqrt[#1]{#2}}
\makeatother
\usepackage[papersize={12in,12in},body={10in,10in},margin={1in,1in}]{geometry}
\pagestyle{empty}
\begin{document}
\fontsize{50.000000}{62.500000}{\rmfamily % Comment out for normal
$\sqrt{D_3} \,\textrm{RMSE}(X, Y)$
} % Comment out for normal
\end{document}
PS - I would like to keep using the physics
package.