I think buying bitcoin using a credit card is not very attractive to me because it incurs a large transaction fee between 3% -6% depending on the credit card and the exchange party. So I prefer to buy bitcoin by using a bank transfer because the cost is not too large so I can get more profits.
Using credit card will surely incure more charges which will not favor a trader, because you have to consider so any charges to be paid before the money finally gets to destination, there are so many charges already on ground, bitcoin network charge, local exchange charge trading fee, withdrawal fee and many more, if we now add credit card fee to it, it will be too outrageous, so I think it is better to use bank transfer as you said.
The issue with bank transfer is that it has to go first through your local exchange that is registered with your countrys domiciled bank, because I dint think you can just make a transfer directly to any payment system that will convert you fiat directly into the bitcoin, but we have to deposit it first into a bank that can only be provided by a third party local exchange.