[xlr8or]

The basic difference are this:
Factory Five: User assembled not factory assembled. Lots of options available to customize to user preference. Build quality will vary based on builder. Reasonable price.
Superformance: Factory assembled with consistant quality, sold as a painted roller minus engine and transmission. Costs much more, endorsed by Shelby if that matters to you.
Shell Valley: User assembled, not that many out there, quality will vary by builder. Reasonable price.
Lesher Motorsports: Mid range price, user assembled.... Not many out there.
Kirkham Motorsports: Work of art, highest price, very few of any out there.