Which is the best app to charge credit cards for Andriods or IPhones?

Long story short, I do part time per schedule work as a Firearms instructor and specialize teaching women how to defend themselves. I don't advertise that much as it is mostly weekend work which averages out to about 16 to 20 instructor hours I log each month depending on the time of year.

The issue is that half the time I go to a gun range to train a small group of clients, a few other ladies ask if they can join the class or if they can take a class right after I'm finished with my clients. Since I don't have a full flown business I work on a cash basis, but 90% of the time the would be 'new immediate clients' intend to pay with a credit card and don't have the cash on them, which means that many decide to reschedule for a later date. So I figure it's time to get an app to charge credit cards. Having heard some horror stories that certain apps are not reliable I figured it would be smart to ask someone with experience in these things.

I have an Android and an IPhone but not much else in terms of business charging equipment. So which apps do you recommend and what type of accounts do I have to set up? Can you link them to a personal checking account or do you need a special merchant account?

There's a company that created a small plugin on the bottom of an iphone (forget the name, but I'm sure searching will find it easily as its popular), so you connect to the bottom of an iphone and you can swipe credit cards through that. Just like a credit card verification machine. Many small businesses use that.

There are several, Square is the oldest of the bunch. They work with either iOS or Android, you just download the appropriate app. The same reader dongle works on both.

Search Google with "take credit cards with smart phone" and you will get a large list.