IPad suggestions?

I am an android user, so I'm not familiar with the different types of iPads. My last Apple product was an iPhone 4 in high school lol

There are a few apps that would be really helpful for my business, but they are on Apple devices only. I can't spend much on an iPad right now, so I don't need the latest one or anything. What should I be looking for though? I do need a regular size one, not a mini. I'm too nervous to buy one used too.