If you're about fancy branding and overpriced appearance mods, then Shelby all the way. You're definitely not getting more performance and offroad capability from the Shelby vs spending that same additional cost on modifying your Raptor through any one of the reputable vendors on this forum.
In addition, I kind of look at the Shelby or the Roush as being targeted at those who just want a turn-key modded truck and don't intend to do much of anything major after the fact. If you still end up dumping money into it other then basic appearance mods than you're defeating the resale value argument.
Plus, when someone blows past you in the dirt or on the street in their non-Shelby modified Raptor are you going to be content in proclaiming your #n of 500 truck while choking on the exhaust fumes and dust kicked up by the non-Shelby Raptor? It's definitely a case of get it if you want it, but don't try to justify it as being functionally better than what you could've done otherwise.