Accounting systems can be a real nightmare for many small businesses. It's worse to be undersold a system than to be oversold one.
Why? Your accounting system provides the information you need about your business. A very basic system will let you know the basic dollars and cents. The more complex ones help control inventory, highlight slow moving lines, give you marketing information etc. so you can make more money. You tend to get what you pay for. A good business consultant can check that out for you.
The more powerful (bigger, more expensive) systems usually require more data to be fed into them, so that you can get more (and better) information out.
If you don't know much about accounting systems, your accountant should be your first contact. She knows your business and your capabilities and should be able to recommend an appropriate type of system. If you're looking at investing more than a few thousand dollars, you should probably consider issuing a Request for Proposal (RFP) to selected potential suppliers.