For 3D machined parts with no finishing specified, the eMachineShop machinist will use discretion whether to vibratory tumble parts or leave parts as machined. It is generally recommended to leave the decision to the machinist.
This finish does the best job of removing sharp edges and burrs and is more economical as it does not require machining chamfers to avoid sharp edges. (Chamfers were however machined in this example.)
This finish has a machined appearance. If you choose this finish it is strongly recommended, for safety, to include in your design chamfers on all edges to break sharp edges (this increases machining time and hence cost). This finish requires special handling which also adds to cost. You can request this finish under Job | Finishing | Machined Finish.
Please note that the finish for each particular design or run will likely vary slightly from the above examples which are displayed only for general guidance.