There are lots of potential causes for your vibration, so lets go down the list.
Number One is wheel/Tire
Balance. Note, Spin Balancing is NOT as accurate as bubble balancing. Because a precision bubble balancing machine can have the vial ground to something on the order of 0.0005 inch per foot. Bad news is because it takes more time to do the
balance about the only bubble balancers still in use are on Racing Teams or old farts like me who know how good they can be. This means that your only choice is to have them spin balanced and there can be a huge difference from one shop to another. I would suggest going to a shop that is "in" with the autocross crowd but I have had good results with the Firestone in Roseville, MI.
Second cause is bad rotors but they are way down the list compared to
Wheel balance. Here the best way to test them is to just buy new rotors and the good news is that it won't break the bank.
Third is suspension wear, as in ball joints and tie rod ends. Here you have to remember that spin balancing is not that accurate, Basically all spin balancing does is get the
wheel balance "good enough" for a suspension in good condition with enough friction to damp out the slight imbalance. If you have ball joints worn to the point of being just a touch "loose" that play in the ball joints or tie rod will act to magnify any out of
balance condition. In addition the condition of the struts will likely be less than optimal if they are the same age as the rest of a worn suspension.
My advice for a solution is like the previous posts, check the
wheel balance. However I would not go to the same shop that did the present
balance, find another shop that has good reviews or recommendations.
PS; the original VW Beetle had a devise attached to the tie rod assembly called a Steering Damper and when they wore out you could get wheel shake severe enough to rip the steering wheel out of your hands if you weren't expecting it. Good news with the Beetle it was a harmonic thing that happened between 35 and 40 mph so hard braking or speeding up could get you out of that shake zone. Good news is they were easy to replace on the Beetle, bad news is I've heard that some Trucks and Suv's are re-introducing these devices. I only mention this because being rather new to the FiST I have no idea at all if they feature a steering damper.