It is better to use one of fast altcoins for transactions bitween exchainges. It's cheaper and faster. I use Dogecoine for this
There are no dogecoins at Bitfinex last time I been there. But you can use LTC which is traded on both of these exchanges and still more so if LTC exchange rates are higher at Cryptopia. But beware of the "small deposit fee" that you may have to pay when withdrawing funds from Bitfinex.