I have no strong feelings either way, though I do love 'square and clean' joints on old knives. All folding knives originally had square tangs, rounding them was a way of reducing wear on the spring which causes the point of the blade to raise up in the frame, and eventually become slack. Pistol grip hafts, often seen on old knives, were another way of covering the raising point of the knife, allowing it to be pocketable for longer. Round tangs were an innovation of French cutlers, and cutlery historian Simon Moore playfully speculates that Sheffield cutlers were slow to adopt the rounded tang, realising that it would lead to them selling less knives!
Since steel is run harder now, and few folks use their knives really hard, with most of us owning more than one, we don't really see the technical advantage of a round tang anymore.