After dealing with quite a few payment processors (traditional and mobile) I have settled on PayPal for all transactions. We've processed tens-of-thousands of transactions using PayPal and have yet to deal with any issues. We are set up with extremely low processing fees (much lower than Authorize.net, Square, etc) and they helped defend us against our one and only chargeback (the customer was attempting to get his products for free and PayPal stepped in and put an end to it).
If you do end up using PayPal, for commercial transactions, make sure you use PayPal's virtual terminal (manager.paypal.com) for any hand entered (card not present) credit card transactions. Should you manually enter the info directly into the mobile app there are additional fees and they will hold the funds for 72-hours.