Tough call, but I'd give a slight edge to the Winner's Board for being a bit more exciting in the heat of the moment. True, the fact you were guaranteed to walk away with something, even if it was essentially banked to be risked later, did give it a bit of an anti-climactic feel, but on the other side of the coin, so does, to an extent, telling them they've won something but had a whole commercial break to think over whether they wanted to take it or not.
This is likely a minority opinion, but the Winner's Big Money Game, on its own, wasn't a terrible end game, albeit a very difficult one; it was just the wrong option for Sale, and would have done much better on a different show where solving puzzles was the primary gameplay.
Were it my call to oversee a revival, my version of the bonus game would essentially blend elements of both accepted end games: essentially, the champion would play a second speed round, having to successfully answer, say, 10 questions in 60 seconds to win the available prize of the day--as with classic Sale, there would be a tier of 7-10 prizes of increasing value that they'd be going for one at a time, probably with a car next to last and a cash jackpot between $10,000 and $25,000 last. Should they successfully win the prize of the day, they could choose to take it--and any other prizes accumulated to that point--and leave, or risk them to go on (if they failed the bonus speed round in that case, they automatically would come back the next day, but that prize would be out of play for the moment). If they made it through all, say, 10 episodes, they would be given the final choice to take everything won to that point and leave, or risk everything for the final game. Lose that, and they go home with nothing; win the last game, and they win everything, including the prizes they missed the first time around, and a grand prize jackpot--$100,000 would probably work best today.