\[ \boxed { {x}^{2}{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) -\sqrt {a{x}^{2} \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}+b \left ( y \left ( x \right ) \right ) ^{2}}=0} \]
Mathematica: cpu = 1.836733 (sec), leaf count = 39 \[ \text {DSolve}\left [x^2 y''(x)-\sqrt {a x^2 y'(x)^2+b y(x)^2}=0,y(x),x\right ] \]
Maple: cpu = 1.622 (sec), leaf count = 60 \[ \left \{ y \left ( x \right ) -{{\rm e}^{\int ^{\ln \left ( x \right ) } \!{\it RootOf} \left ( \int ^{{\it \_Z}}\!-{y \left ( x \right ) \left ( {{\it \_a}}^{2}y \left ( x \right ) -{\it \_a}\,y \left ( x \right ) - \sqrt { \left ( y \left ( x \right ) \right ) ^{2} \left ( {{\it \_a}}^{2} a+b \right ) } \right ) ^{-1}}{d{\it \_a}}-{\it \_b}+{\it \_C1} \right ) {d{\it \_b}}+{\it \_C2}}}=0 \right \} \]