Reviews will give you an insight. When people have negative experience, they tend to share it.
It also depends on the kind of business you are doing. If you are into risky businesses, or if your business is considered as risky, you may want to avoid the top payment gateway's as they will block your account down the line and freeze your money.
I recently discovered Payfaci, and I am in the process of getting my kyc verified. They have very low transaction fees and frown at fraudulent chargebacks which make them suitable for online vendors.