Somebody has quoted you a lower supply rate and you want to know whether it is actually a better deal. That is a fair question and it has a definite answer, but the answer is not on any comparison chart, because a rate is only half of a price. The other half is your own kilowatt hours, and nobody has those but you.
What a supplier can and cannot change
In Illinois you can shop the supply half of your bill: the energy itself, priced in cents per kilowatt hour. You cannot shop the delivery half. ComEd carries the power to your building no matter whose name is on the supply line, and the delivery half is set by a filed tariff.
That single fact bounds the entire decision. A supplier is bidding on one part of your bill. Before you compare offers, it is worth knowing how big that part is, because a very good price on a small number is still a small number.
Take your last bill and add up the supply side, then add up the delivery side. If delivery is the larger of the two, the best supply offer available to you is competing for the smaller half, and the demand charge sitting in the delivery half is untouched by every offer on the table.
Why the lowest advertised rate is not the cheapest supplier
Once you know supply is worth fighting for, the comparison itself is where the money is lost. Four things decide whether a lower rate produces a lower bill.
The rate you are comparing against. The number to beat is not the utility's published price to compare in the abstract, it is what you actually paid per kilowatt hour last year. Divide the supply dollars on each bill by the kilowatt hours on the same bill. That is your real supply rate, and it is frequently not the number you think you are paying.
What happens after the introductory term. A twelve-month fixed price that rolls to a variable rate is two prices, and only the second one is open-ended. The comparison that matters is over the whole term you will actually be on the contract, including the months after the promotional period ends.
Whether the price is all-in. Some offers quote energy only and pass through capacity, transmission, or ancillary costs separately. A quoted rate that excludes a pass-through is not comparable to one that includes it, and the difference shows up on the bill rather than in the pitch.
Your own shape, if the offer is indexed. If the offer is tied to hourly or block pricing rather than a flat rate, then when you use power matters as much as how much you use. A building that runs hard on summer weekday afternoons and a building that runs overnight will get very different results from the identical contract.
The arithmetic, on your own numbers
You can settle this at your desk with what is already in front of you.
Pull twelve months of bills. For each one, write down the kilowatt hours and the total supply dollars. Multiply each month's kilowatt hours by the offered rate, add whatever the offer passes through separately, and compare that total to what you actually paid. Do the same for the months that would fall after any introductory period expires, at the rate that applies then.
The answer is a dollar figure for the year, not a rate, and it is specific to your building. Two businesses on the same street with the same square footage can get opposite answers from the same offer.
When the answer is "none of them"
It is worth saying plainly that a legitimate outcome of this exercise is that no offer beats the default by enough to be worth signing a term contract over, and another legitimate outcome is that the supply half is small enough that the whole question is a distraction from the delivery half.
Neither of those is a disappointing answer. They are the correct answer for a meaningful share of commercial accounts, and finding out costs you an hour with a stack of bills.
Who is the cheapest electricity supplier in Illinois for a business?
There is no single answer, because a supplier quotes a rate and your bill is a rate multiplied by your own usage, then added to a delivery half no supplier touches. The cheapest supplier for your business is the one whose offer, applied to your last twelve months of kilowatt hours over the full contract term, produces the lowest total.
Can I switch electricity suppliers and stay with ComEd?
Yes, and you have no choice about the second part. ComEd delivers the power regardless of who supplies it. Switching changes the supply portion of the bill only.
Is a fixed rate better than a variable rate for a commercial account?
It depends on what you are buying. A fixed rate buys certainty, not necessarily savings. The comparison that matters is the fixed offer against what you actually paid over the same period, including any months after an introductory term when the price changes.
Does switching suppliers reduce my demand charge?
No. The demand charge is billed on your highest single interval and sits in the delivery half of the bill, which is set by tariff and is not shoppable.