Do I have a tire problem?

About 9 months ago I needed new tires on my Mercedes E350. I had a set of Capitol UHP's put on them but something was not right. I felt a wobbling in my steering Wheel at around 60 -65 mph. I took it back a few times to get the tires rebalanced and it was a little better everytime but never quite the same. At the time, I just figured I was being picky and forgot about it. Last week though, I got to thinking about how it bugged me so I took them back. After rebalancing and rotating, the wobbly steering was still there. Then they looked at my front end and told me there was a little play but nothing major in the bushings. Finally today they put a new set of Capitol's on and charged me $350.00 (mainly because it had been 9 months). They also said my tires had some "feathering" on them where the tread was worn more in some areas. After putting new tires on, I still noticed the problem and called the tire shop. They are now offering to put a new set of Hankooks on at no additional charge. I guess what I am asking is could it be the front end, Capitols etc...etc...? Are the Hankook's a good tire or should I be pushing for something better (even if it does cost me more) what do you think? Please let me know..