i would use Dogecoin if possible, if not Litecoin.
Dogecoin transaction fee is 1 Doge equal to ~120 satoshi
LTC transaction fee is usually about equal to 1000 satoshi if i recall correction!
no matter which altcoin you choose you should have these things in mind:
- make sure the wallet is active and has balance before withdrawing also make sure the other wallet you are sending to is active and healthy.
- make sure the names of the markets match. sometimes they call an altcoin XYZ in both exchanges but they are two different things. (not true about the coins i named though such as XRP, LTC, Doge).
- and finally doing this with altcoins you may save up on transaction fees but you may lose a lot of money because of the spread price between buy and sells.
let me give you an extreme example for better understanding:
if Doge is 110 satoshi then it is that on both exchanges.
the bids are on 109 and asks on 110. you buy from 110 then transfer to other place and sell at 109 which means 0.9% loss. if you buy 1
BTC you lose 0.009
BTC on this difference alone. now add to that 2 trading fees which we assume both are 0.2% which is 0.004
BTC.
in this process you spend 0.013
BTC to save up on paying 0.00020000
BTC bitcoin transaction fee (aka withdrawal fee).
edit:
Most exchanges charge higher fees for bitcoin , with the high fees and mempool problems, ripple might cause you less in fees
i am not using either of these exchanges OP mentioned but someone once said polo charges 10K for BTC fee and i know that bittrex charges 20K for BTC fee! and by the way they pay a lot higher transaction fee themselves no matter what they take from you!