17" Tires cost less than 18".
Performance wise, the 18" should be better as the profile is lower making for less of a squishy ride.
17" has a high profile and provides that extra cushion with the pot holes.
All of the tires you list are great performers. Further posts in this thread will have members touting they swear by one of these brands over the other.
Check Tirerack.com for user reviews or Consumer Reports. I believe they rank the Michelin the top performer and you also pay the premium price.
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