It depends on aircraft type. In an old airbus the speed is controlled by the autothrust and the V/S is the pitch mode. I generaly would select the speed about 5 knots less as this keep auto thrust changes to a minimum,but you must be prepared to accept some speed variation around your target.
You can use speedbrakes and V/S but you need to be aware that this can lead to the autothrust in some circumstances increasing thrust and fighting against the drag of the speedbrakes. This is obviously not very fuel efficient.If you wish to increase your rate of descent I would utilize a mode which gives idle thrust(LVL Change or OpDes),and extend the brakes. If this is still not enough then I would either increase speed or alternatively extend the gear depending again on circumstances.
Last edited by tubby linton; 8th Jun 2012 at 16:14.