The both of them have their various potentials and advantages it all depends on  how long you want to keep it there, if it is money you intend keeping it for a very long time I mean 3 to 5 years time then bitcoin is just the best option to pick but if it is money you will be needing anytime soon then USDT is just the best for that purpose. However either of these is far more better than keeping your funds in our local currency naira, because naira can mess you up at any point.