I'm going to be a fool and wade into the engine comparison. Y'all can feel free to berate me and scream, "Off with her head!"
1. There are folks who love each one of the four motors--7.3L diesel, 6.0L diesel, 6.8L V-10 gas, and 5.4L V-8 gas. And there are folks who have the same level of feeling--except in the opposite direction--for each of these powerplants. What is right for one is dead wrong for another. YMMV.
2. The diesels generally get better fuel mileage than the gassers--especially offroad. YMMV.
3. The diesel motors tend to be more expensive than gas with respect to maintenance. YMMV.
4. The diesels are louder than the gassers. Whether this is good or bad or meaningless is up to each individual.
5. The 6.0L diesels have something of a history of issues. An internet search will provide you with tons of information on this. There are various approaches to "bulletproofing" to address these issues. YMMV.
6. The 5.4L gasser is the least powerful of the four. Most of the 5.4L rigs also have the 75R trannie, which is the lightest duty of the group. Some folks want the additional grunt of the V-10 or the diesels; for others, it makes no difference. YMMV.
7. Generally speaking, the 5.4L gasser tends to get better fuel mileage than the V-10. YMMV.
8. Some folks consider the 7.3L diesel the holy grail of Econoline powerplants. YMMV.
9. Other folks do crazy-a&& stuff like stick a Cummins diesel and Allison transmission into their Econoline. But I digress...
Read, talk to people, drive a bunch of rigs, ask questions on the Forum, and figure out which tradeoffs are best for you. Match the rig you buy with the uses you will put to it. The right rig for you is going to be very different from the right rig for someone else. We all use these vehicles differently. Daily drivers have one set of priorities; weekend rock crawlers another; desert racers still another. Think carefully about your use case, and match accordingly.
Good luck, and enjoy the search.
OMG, the Silver Streak is Sold!
2006 SMB EB45ish.
5.4L, QuadVan 4x4
Ready to Rumble!