Please recommend me mode of transportation
Metro?, bus, taxi?

I'm a Southsider so I know much more about Midway. But you would take the Metra or a cab/shuttle. Call your Westin and see what shuttle they suggest, if any. Cabs will be much more money.

Check out the Metra from O'Hare and it will tell you its station address downtown and you can see if that is doable with luggage.

You can take the Blue Line Subway from O'Hare to Clark/Lake. It will cost $2 and take about 45 minutes. Your hotel is about 3 blocks north on Kinzie between Clark and Dearborn Streets.

To reach the Blue Line, follow the signs from the baggage level of Terminals 1-3 that say "Trains to City."

A shared van is $25 and a cab would be around $40. Travel time would depend what time of day you're arriving.

The subway is your best option. If you will have lots of luggage or the weather is bad, you can hail a cab when you arrive at Clark/Lake for only a few dollars.

From looking at a transit map, it looks like you can take the Blue Line train to the Clark stop. From there, walk one block east of Clark to Dearborn, turn left and walk two blocks north on Dearborn (crossing the river), and the Westin is there at 320 Dearborn.

It sounds doable via train/walking. Of course, it would depend on how much luggage you have.

Hope this helps...

Oops--should've refreshed. Citylghts's response was sooner and more comprehensive...

If you're going to be there for a couple days and will be using the el more than twice a day, buy a visitor pass at the el station -- there's an orange machine that says "Visitor Pass" just as the airport connecting walkway puts you in front of the trains. You can get unlimited rides on the subway and bus (including your trip from ORD-downtown) for like $5/day.

Thanks to all of you for taking the time to help me.