For me it all comes down to the synergy of the product features. the on-going enhancement and the support you receive from the community.
And in Spiff's case this synergy deserves 5 stars, no question about it.
Ultimately when you build your process architecture you want to be sure you have as much freedom and flexibility from the product you use and if you can add to that an opened partner-like support service from people with process passion, then I'd say you have a winner.
