I would try stiffening the rear first if you drive mainly on the street, If you track it it would be a toss up, the good thing is you can experiment. For me the rear is easier to get to for adjustment.
My experience in replacing the rear mufflers is it is likely to drone. You are going to need to use the stock or good resonator to keep the drone down.
Use the muffler to replace the stock resonator. picks up some torque,
keep the rest of the system as is. Not a loud option, will quiet down the exhaust, the true x inside the muffler increases torque.
The stock 5.0 exhaust bolts right up, makes it sound like a mini v8, not loud, just sounds better. Get a used entire exhaust with a single muffler outlet. Paid $100 for one off Facebook market place.
Shelby gt350 194# front springs, Ford Racing front struts, Koni Active rear shocks, sway bars front and rear set of your choice- Steeda, Ford Racing, etc. You will have what you want.
Added 2 stand alone tweeters in the rear with self contained housing to brighten the sound. Ran the wiring off the rear speakers. Housings were stick on to the rear sail panels. Improved the sound quality. Also runnig a sub in the trunk and resest eq with Forscan. Finaly satisfied with the...