Amin- Nobody can make an intelligent cart recommendation without having lots more info. Where you are located. What and how you sell. That sort of thing. Also, I think you are about to create a very big headache for yourself by putting the cart before the horse. By that I mean you are creating a compatibility nightmare. Authorize.net may or may not work with whatever merchant account network you select, and since getting written for a merchant account will be your hardest challenge, you need to set up THAT first, then based on that selection move onto a gateway and cart---not vice-versa as you are doing.