This only apply to USA. I don't know the process for other country.
Square has a flat rate of 2.7 for cards that are swipe and 3+ for manual entry. This work for any credit and debit card.
With a traditional having a merchant ID, you pay interchange + rate + misc charge. To give you an example
a debit card would be around 1.5%
a credit card with no rewards would be around 1.5% to 2%
a credit card with reward or point would be around 2% to 4%
American express is about 3.5% and higher
Here's what I'm currently doing
First I ask if I can do debit.
For American Express, discovery and Business card I used Square.
For online I use Paypal.
Otherwise I use the traditional way. If you opt to have the traditional way, make sure you have the volume. If not start with Square.
Paypal has the same device as Square but rate is a bit higher 3.1%. I carry it as a backup but never used it yet.
So far no complaint from the user about square but I have read a lot of bad reviews for square. Been using it for over a year