I have a V6 and my mom has a V8. I've driven both, and would be happy either way. I love my V6, and I love my mom's V8. The V6 has a timing chain, and the V8 a belt. Since you're looking for one under 100k, it's more likely the belt won't have been replaced yet. That's extra money spent after you buy the truck.
One MAJOR thing to think about is what you're going to use it for.
If you're just going to use it as your DD, then the choice is really left up to personal preference. I get the same, if not LESS, MPG as my mom's V8. The choice is really up to you.
If you're planning on a nice Off-road rig, it's, once again, up to you. The V6 has more available engine mods, but the V8 (both trucks in stock form) will produce more power and torque than the V6.
If you're towing, DEFINITELY a V8. The V6 is more than capable, but that extra torque will have no comparison in comfort of towing.
General Pros and Cons:
V6:
Pros:
- Timing Chain
- Lighter
- (Typically) Slightly better fuel economy
- Selective 4WD
- More Engine mods available
Cons:
- Less Power and TQ
- More problematic w/ Head Gasket (Not likely, though)
- Although it sounds GREAT, you can't beat the rumble of a V8
V8:
Pros:
- More Power and TQ
- RUMBLE RUMBLE RUMBLE
- Iron Block
- (Better?) Head gasket
Cons:
- Heavier
- Full-time 4WD
- Less available engine mods
- Timing Belt
- Cracking Exhaust Manifold
- Less Engine Bay Room
Honestly, they're both great engines. But with that extra performance of the V8, comes more maintenance. A lot of the cons are also correctable, but usually at the cost of a lot of money. It all comes down to what YOU want and what YOU're doing with the truck.
Good luck with the buy, and hope to see you around here some more soon!