\[ y(x) \left (a^2+\frac {a f'(x)}{f(x)}-b^2 f(x)^2\right )-y'(x) \left (2 a+\frac {f'(x)}{f(x)}\right )+y''(x)=0 \] ✓ Mathematica : cpu = 0.0576106 (sec), leaf count = 49
DSolve[y[x]*(a^2 - b^2*f[x]^2 + (a*Derivative[1][f][x])/f[x]) - (2*a + Derivative[1][f][x]/f[x])*Derivative[1][y][x] + Derivative[2][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to c_1 \exp \left (b \int _1^xf(K[1])dK[1]+a x\right )+c_2 \exp \left (a x-b \int _1^xf(K[2])dK[2]\right )\right \}\right \}\] ✓ Maple : cpu = 0.492 (sec), leaf count = 74
dsolve(diff(diff(y(x),x),x)-(diff(f(x),x)/f(x)+2*a)*diff(y(x),x)+(a*diff(f(x),x)/f(x)+a^2-b^2*f(x)^2)*y(x)=0,y(x))
\[y \left (x \right ) = {\mathrm e}^{\int -\frac {f \left (x \right ) {\mathrm e}^{\int -2 b f \left (x \right )d x} {\mathrm e}^{2 c_{1} b} b +b f \left (x \right )-{\mathrm e}^{\int -2 b f \left (x \right )d x} {\mathrm e}^{2 c_{1} b} a +a}{{\mathrm e}^{\int -2 b f \left (x \right )d x} {\mathrm e}^{2 c_{1} b}-1}d x} c_{2}\]