Frankly, either one will serve you well. Most conversations on this topic will end up in some sort of brand flame war.
I will freely admit I am biased towards the Fords, but thats what happens after nearly 350,000 miles on my last (97 F150, sold with 163,000) and my current F150 ('99 F150 with 178,000 currently on the odometer).
In generalities, Ford tends to build a heavier, more work oriented product while GM has typically produced a more "peppy" and comfortable ride. They both will work and work well. In our work fleet, we buy an occasional Chevy for one reason or another (such as a need for a Suburban) and just to verify we are still getting what we need from Ford and there isn't a better mousetrap out there. We still have not found a reason to switch the truck fleet over to GM from Ford, but also haven't noted huge issues either. So, we stick wioth what we know. GM's tend to get slightly better fuel mileage historically, as their engines were tuned for more car like performance (admitidly how most trucks are used today)and their trucks were overall lighter.
My trucks are not fast and are not hot rods. I can guarantee that they will work hard ang get the job doen though without too much fuss. My F150's have been the most reliable vehicles I have ever owned, and considering how they have worked at times, that is an accomplishement by itself!
If I were buying new, I'd stay as far away from Government Motors as I could for personal beliefs. For a used vehicle, given you want a work style truck, I'd look to see what I can find first, and it may become a case of finding what you want, and accept whatever brand you find the deal in.