Crestron is typically going to cost more.
The biggest issue that most control systems have is that you want support for it 5 or 10 years down the line. While many companies have control systems today, quite often their control systems are only partway figured out and not entirely supported. So, you get a great deal now. But, in 3 years, something goes wrong. You call up the manufacturer/installer and they say "Wow, really sorry, but that company stopped making those products last year and don't have replacement parts."
In comparison, Crestron has been doing control systems, and JUST control systems for what... 20 years? More? I have a control system that is over 6 years old - it works great and is still fully supported by the software that is out today. A programmer could come to my house, program it from scratch, and leave - without digging through archives or anything!
As said though, this is not cheap.
While I can't speak for Elan, I can speak extensively about Crestron as I am a Crestron programmer.
Other Crestron plusses (in general): True customer support and service. Including a 3 year warranty on products.
Phenomenal reliability: These things are used in war rooms in the Pentagon! Bullet proof reliabilty at all levels.
50% of their business is residential - and they do a TON of business.
They are a control system company - from the start, to the finish, that's what they do. If you have issues, they have US support offices which are there to support the installer and get you up and running.
If you have more questions or want more specifics about something, feel free to PM me and I'll be happy to go into details with you about any of it.