Actually, It depends on the hydro set-up, and what type of soil. However, soil is easier to maintain, and cheaper, but there's nothing better then weed grown in some nice organic soil if given perfect growing conditions. Hydro is often expensive, but if done right can provide excellent bud too. It depends on the experience of the grower, and the conditions the plant receives. Basically soil or hydro makes no difference, weed is grown better when given the best care.