first of all, are you a buyer or a seller?
By convention in Illinois the seller purchases title insurance to protect the buyer (the "owners" policy) and the buyer purchases title insurance for the mortgage lender (the "loan policy.") for a representative chart of costs, see http://wasserlaw.net/Real%20Estate/Title%20Rates.htm.
as a seller, you have NO obligation at all to use the title company selected by your attorney. in fact, you can use whatever company you want. your attorney cannot legally "force" you to use any specific company and you are supposed to be able to choose. that said, most real estate lawyers have a financial relationship with (or at least a strong preference for) one company or another. they will, as a GENERAL rule, try to steer you to the company that pays them a fee (for work they contrubute to the title process). this is perfectly normal here. it is the way we keep our fees as low as we can.
many lawyers maintain affiliations (agency relationships) with multiple title companies. (ok, as a matter of self-promotion, at least i do).
and with all that said, nick is 100% correct; the price differentials are pretty modest from company to company (less even than the "couple hundred" the he quotes...)
as a buyer, the fact is that it is almost always cheaper to simply follow along with the seller and use the same title company for the loan policy. i have only seen three instances in 23 years where it was cheaper for the buyer to go somewhere else..,..alll three, very unique situations.