Given the choice between a 96-98 GT 4.6 and a 95 GT 5.0 with similar condition & mileage, I would take the 95 GT 5.0. Here's why:
1.) The stock 96-98 model two valve 4.6 engines lack low end torque that make the car fun to drive. Stand on the gas, and the engine has to wind up above 3500 RPM before it starts to pull good.
2.) The 4.6 engines are harder to work on. The added complexity of overhead cams with the chains and drive mechanism makes a head swap or head gasket replacement a major ordeal.
3.) The stock 96-98 2 valve 4.6 heads have such poor flow characteristics that major work to the heads is needed to get them to flow good. Most of the time that means replacing the heads with ones made in 99 or later.
4.) There are fewer budget and junkyard add ons for the 4.6 engines. You can't go to the junkyard and come back with a pile of inexpensive parts that will make more power.
5.) The 5.0 engine is easier to work on and they are very durable.
6.) They definitely have lots of low end torque that makes them faster in standing start or low speed acceleration. Quicker off the line and to 60 MPH with comparable engine configurations.
7.) You can increase the cubic inches of a stock 5.0 to 347 Cu in with an overbore and a stroker crank. There is no way you can do that with a 4.6 engine.
8.) There are lots of speed parts that can be bought cheaply.
9.) The junkyard is a goldmine for speed parts. Find a 95-99 V8 Ford Explorer or Mercury Mountaineer and pull the heads, intake manifold and throttle body and you have a backyard bolt on that can add 30-40 HP. It should cost less than $500 for the engine parts. Add another $350 to have the heads reconditioned and for gaskets and other small parts. Top that off with some good headers and you have a great driving street/strip car for not a lot of $$$.