Dolphin is currently kool shit. I can come up with a proper acronym if given time. Used to play this game with family all the time when on trips or bored, state a random word and make an acronym for that word.
To answer OP, with latest builds use D3D11 or OGL, if you can't use D3D but can use OGL, use that instead. If you can run neither maybe v4.0 still has D3D9, if not then v3.5 however you'll likely forfeit forum support if you use older unsupported builds. With proper hardware OGL is faster in recent builds than D3D11 however I don't think your hardware is adequate enough to benefit from speedups with OGL.
To answer OP, with latest builds use D3D11 or OGL, if you can't use D3D but can use OGL, use that instead. If you can run neither maybe v4.0 still has D3D9, if not then v3.5 however you'll likely forfeit forum support if you use older unsupported builds. With proper hardware OGL is faster in recent builds than D3D11 however I don't think your hardware is adequate enough to benefit from speedups with OGL.