I just got a Park Truing stand and I am anxious to start building some wheels! I started reading Sheldon's (may he rest in peace) wheel building article along with a '77 published book by Robert Wright- "Building Bicycle Wheels". There is a significant discrepancy regarding starting the Key spoke (as a trailing spoke) on the drive side of the rear wheel. Wright says to run it on the outside of the flange; Sheldon says on the inside (because of possible chain binding issues). I am inclined to defer to Sheldon for obvious reasons. I intend to build 36 spoked, x3, wheel.
Which is best in your opinion? Are there any reasons why one would opt for one set up or the other?

This is a religious debate.

Sheldons method is good for touring cyclist/people who are not concerned with wheel performance. If you are do it the 'Wright' way.

Use 3x and thats it dude. Reliability is the key in my opinion.

If I remember right, Sheldon stated his preference but said that it really doesn't matter much, either way. And I agree with that.

4x is every bit as good as 3x. You can choose between them based on availability of the length to make it work. I happen to think 4x looks cooler, but that's just one person's opinion.

For an average guy doing average riding on a decently built bike of average configuration, the margins in the design are so big that nuances like that simply won't register.
I like SBs line of reasoning, but as long as spoke tension is OK it's not the deciding feature that'll either make or break the wheel. Whether it'll hold up or fails is much more likely to be down to other issues.

If Sheldon's way has some advantage to avoiding serious damage from a dropped chain and you don't want to run a spoke saver disc (AKA "dork disc") then I'd say follow Sheldon's way. A chain dropped down between the last cog and the spokes can cause a really bad day. I know because despite my care it happened and I had to relace a blown wheel due to following fashion rather than common sense.

If you choose the sensible but less fashionable course and use a spoke saver disc then run the key spoke either way according to whim. ALL my bikes since that time have proudly worn their "dork discs" and to hell with any that say they are not needed.

Mavic built up sets of wheels using the different possibilities. Mirror image, opposite pulling spokes inbound and outbound. After letting riders use them for a while they found that the mirror image pattern with the pulling spokes outbound had the fewest problems with broken spokes.

So you are saying the method outlined by Robert Wright is the best, then...