I don't think there is any significant advantage in either one.
In my live portfolio, I don't even wait for the uptick anymore, I enter position whenever I can as long the Z-score exceeds the threshold (it behaves like the uptick mode, but in addition it has advantage if you trade more pairs at the same time and you have to allocate your account margin in a smart way). In PTL Trader this mode is called Simple. It is not available in backtest system, because for single pair, it behaves quite like the uptick mode.