Dude! You thought it would be EASY?
1. Determine what you will spend. That's easy - $5K
2. How much cooker do you need? Not so easy but figure out how much you will cook on 90% of your biggest sessions.
3. Wood, charcoal, pellets?
4. Do you need a trailer/axle?
5. Sit in a chair and whine a bit!
All the cookers mentioned and plenty that aren't will get the job done for you. My only regret with my Kingfisher is I didn't buy the bigger 6 shelf rotisserie model. My 4-shelf has taken care of the 90% (#2 on the list) and I've cooked pulled pork for 400 folks on my cooker.
Now, that being said, I'd kill for an FEC500 or Jack's Old South Shoulder or pig cooker. The FEC for volume (I happen to love rotisserie shelves) and pellet convenience, the JOS for volume and INSULATION. Of course, you pay for these features. I live and cook mostly in FL so my single skin cooker has been ok, but there have been times I would have killed for an insulated cooker.
So, keep looking and kicking the tires. Nothing beats a trip to a cook off, or a dealer/fabricator. Check out your local area - you might be amazed at some of the work being done in your own back yard! My next rig will probably come from a guy in Lakeland that I met at one of my first cook offs.