What year should I for a daily driver?

I plan on keeping it all oe

92 and newer have 4.6L V8,will get you much better economy and hiway performance due to new body style. Down side is parts usually cost more than pre 92's. Mine's a 99 , 98 and newer have Awsum handling and performance (240hp)

It depends on what you REALLY want out of it.

For fuel economy and cost, I'd ONLY get a 1997 with single exhaust (LX or Base). Cars with duals have deeper gears and get lower mileage. You can expect 20-22 round town, and 26-30 all highway on a car with single exh., and they are VERY relaible.

i ended up getting a 98 mostly because of the body.

I just came from a 3hr drive on the I-80 (little traffic) and got an avg 22 mpg with me, 4 passengers, and about 100 lbs of luggage. I think 22mpg is great for a V8. I was driving 75-80 most of the time. 70 seemed like a good speed for most mpg.

Current mods are...

single 50 series flows with stock piping (almost sounds like a stok 4.6 stang)

removed snorkel and replaced for 3" diameter tubing

That's not bad, but you should be able to get 24/25 in pure freeway driving and on non-oxygenated fuel. The '98 up cars are bricks compared to the pre'98 cars, so you'll loose about 2 mpg to them in otherwise identicle cars.

"non-oxygenated fuel" ?

Oxygenated fuel refers to gasoline with methanol content. It has a some what lower btu (energy)content than straight gasoline. But burns cleaner.
I have not been able to measure any milage change using either. The methanol is free fuel line deicer in cold climates!