The consumer has the choice between buying from their local utility (Local Distribution Company - LDC) or from one of the deregulated suppliers. There is a large range of contract options from a variable price to 1,3 or 5 year fixed prices. Electricity provider switching is difficult once the consumer is in one of these contracts, unless they are close to the end of a fixed price contract. However, as of January 2010 there is a maximum termination penalty allowed.
When it comes to the electricity itself, there is no difference at all. A cheap electric supply is the same electricity, it's simply provided by a new supplier (unless you opt for green energy - more on that here). As suppliers buy and generate different sets of energy they also have different prices. What's more, you might be on a tariff that is simply more expensive, such as a standard tariff. If you decide to switch electricity don't equate a lower price with worse service.