\[ -(f(x)+3 y(x)) y'(x)+f(x) y(x)^2+y''(x)+y(x)^3=0 \] ✓ Mathematica : cpu = 0.0516968 (sec), leaf count = 75
DSolve[f[x]*y[x]^2 + y[x]^3 - (f[x] + 3*y[x])*Derivative[1][y][x] + Derivative[2][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to \frac {-\int _1^x\exp \left (\int _1^{K[2]}f(K[1])dK[1]\right ) c_1dK[2]-c_2}{\int _1^x\int _1^{K[5]}\exp \left (\int _1^{K[4]}f(K[3])dK[3]\right ) c_1dK[4]dK[5]+c_2 x+1}\right \}\right \}\] ✓ Maple : cpu = 0.062 (sec), leaf count = 38
dsolve(diff(diff(y(x),x),x)-(3*y(x)+f(x))*diff(y(x),x)+y(x)^3+f(x)*y(x)^2=0,y(x))
\[y \left (x \right ) = \frac {-\left (\int c_{1} {\mathrm e}^{\int f \left (x \right )d x}d x \right )-c_{2}}{\int \int c_{1} {\mathrm e}^{\int f \left (x \right )d x}d x d x +x c_{2}+1}\]