Used. I've been looking for a very clean, low mileage 2004-2008 Ford F-150 under $10k. I think it's the best value and meets my needs. Currently i'm waiting for year end bonus at work and tax returns so I can buy with cash.
I have around 145000 on my 06 5.4 currently. Previous owner did spark plugs but if you're a mechanic I'm sure you can handle the spark plug issue if it comes about. All of my issues have been minor. I am also in the Midwest with lots of salt and rust buckets here. Surprisingly mine has very minimal rust. Truck had 110k on it when I got it 5 years ago.
Coil boots/coils(otherwise misfires in rain, super easy fix) you can replace all coils for cheap but for me I just needed new boots on a few.
4wd solenoid and a tap on the 4wd motor when I first got it, no issues with 4wd in the 35k miles I've owned it since.
Power steering pump/line, cheap fix(not a common issue at all)
And a couple studs rusted/broke on my exhaust mani recently and now leak.
You might not have any of these issues.
All orignal transmission and engine. I haven't had any of the cam phaser / excessive ticking noise and I'm not easy on my truck. I also use Motorcraft 5w20 and Motorcraft oil filters(have to use them due to the special valve they have)
I would highly recommend a programmer on it. Otherwise the pedal is very laggy and the shift points aren't real great. But they're awesome trucks. My dad and uncle previously had that generation 5.4 and loved it too. We have a 06 work f150 with the 4.6 that lasted 230k on the same engine towing a trailer loaded down with tractors its whole life.