> **if we compare blockchain transaction fee with traditional centralized banks protocols (Visa or MasterCard) which one has more affordable transaction fee?**

That isn't necessarily a relevant comparison. At least, not for me.

I make most purchases online using a debit card. The bank doesn't charge me a fee for this type of transaction.

I make some regular payments (monthly bills etc) using online banking. The Bank doesn't charge me a fee for those transactions. I use something called the Faster Payments System (FPS) which usually takes a few minutes for the payment to show up in the recipient's account. The Banks charge each other a flat fee (GBP 0.03) per transaction but that fee doesn't appear anywhere in my bank statements. 

Since Bitcoins were conceived, at least partly, as an electronic equivalent to fiat cash, you can also compare the Bitcoin transaction fee with the transaction fee you pay when purchasing something using banknotes and coins - again zero.

So it is only certain forms of payment that result in fees for the purchaser using payment systems supported by banks. In many cases the apparent fees to the purchaser are zero. You can avoid most transaction fees with a little care.

For businesses or a retailer, fees will be more evident.

For a consumer making a purchase, Bitcoin transactions might only be cheaper where the the transaction

- can wait for several blockchain confirmations or
- is one where the recipient takes the risk of trusting it will confirm and
- involves no conversions to fiat (e.g. retailer has a bitcoin wallet)
- involves no use of a BTM (Bitcoin ATM)
- involves no payment processor (e.g. Bitpay etc)
- is a higher value transaction
- where you cannot pay in fiat banknotes
- where you cannot pay using fiat online-banking or fiat debit card
- where the alternative would be a fiat credit-card that you don't pay off in full when due -- or some other relatively expensive method that is usually avoidable in my part of the world.

of course there are costs to running any payment system, however for payments in fiat currency, in my part of the world, those costs are paid indirectly by everyone *regardless of their chosen method of payment* - so they are mostly not a factor in choice of payment method.