The plowing route is easier, possibly a little deeper. but I think the end result of a tiller is hard to beat.

If you are planting a small 2 acre garden you can get a rototiller attachment for your tractor and till your garden up. Either way would work. On our garden we run the tiller attachment through the garden then use the plow to make rows.

rotary tilling can be a 1 step operation and gets the soil turned/mixed to about 6 inches. plowin turns the soil over without mixing to from 6-10 inches(8 is most common). Disc harrowing breaks up and mixes soil and residue while compacting the soil. There are several types of harrows, all have roughly the same effect. Either trotary tilling or plowing can be the right way to go, just depends on soils and preference.