The only deck competition I ever won was Alongi's Nomad Mythmaker contest. I built the deck not to be the 'best deck,' but the 'most attention-catching.' I ended up using many different synergies to create a horrible combo deck that used about a dozen cards in the process of making its combo 'go off,' including four Nomad Mythmakers, one lynchpin of the combo. Did I make a competitive deck? No. I've not even been able to build it on Magic Online to see if I can 'go off' anywhere other than solo on apprentice. However, was I competitive when I made the casual deck? Possibly. However, I don't see how a contest other than Magic really enters into anything.