Aftermarkets may not have the same damping coefficient and may cause some
variation in ride and handling quality. I wouldn't think it would be
excessive, though. If they're quality struts and properly installed, I
cannot imagine it'll hurt anything other than your wallet.

You could try rotating the tires and seeing if it makes a difference. If
so, you're looking at a wheel/tire issue. The largest problem I have with
replacing the struts is the reason they were recommended (mileage). So
far, you've posted nothing to indicate that someone has checked something
on your car and found something wrong. If you want your car fixed
properly and expediently, that's what you want. Someone needs to perform
some sort of diagnosis and find something actually wrong (e.g. worn tie
rod ends, feathered tires, bent wheel, whatever) and start there. It's a
much more scientific way of making your problem disappear than *repair x*
is recommended at *mileage y*. While those recommendations may or may not
be valid, there's no reason to expect they'll address your issue unless
there's an actual problem found that interrelates the recommendation and
the problem.