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I think using altcoin is more favourable as even if you lose out it will be that altcoin and not bitcoin which can grow quickly whenever some news come in as this is the king of all coins . Bought everyone has different reason to play with particular coin.
Obviously, its easier to accept a loss if you bet in altcoins, but I want to keep my balance in BTC. But for the withdrawal, it is better to use transactions in altcoins, because their cost is lower.
You still cannot avoid the cost because in the process of keeping your balance on bitcoin and later exchanging it back to altcoin, you will still have to pay some fees for it, while you still pay for altcoin fees too when withdrawing, so by the time you look at the whole thing, you will realize that it is almost the same thing, so I think it could even be better to just maintain one coin and that coin should be bitcoin since it is still the most recognized and the most reliable coins in the market.
I even think that most gambling site accept bitcoin far more than the other coins, except the sites that purposely created their own altcoin for gambling alone, which they will have to impose the coin on their players, but for every normal sites, I think that bitcoin is still the most used.