I'd say QPainter::drawPolyline() is a good option (or QPainterPath::addPolygon). You can use QPolygonF to contain your points. Then you just pass this to the QPainter's drawPolyline
function.
QPolygonF polyline;
polyline.append(QPointF(x, y)); // add your points
painter->drawPolyline(polyline);
or
QPainterPath painterPath;
painterPath.addPolygon(polyline);