tl;dr
For CRM application proxying, load balancing and other magic like IP filtering, use Application Request Routing. To securely publish ADFS and CRM servers to the internet, use Web Application Proxy.
Eye-watering details
If you’ve been following our posts on inventive use of ARR, you know that this technique is specific to IIS. If you have strict rules that prohibit placing any domain members in DMZ, this technology does not help you to publish ADFS server that would be a part of any IFD deployment. The good news is that IFD bible has just been updated to include official confirmation that Web Application Proxy, available in Windows Server 2012 R2, can be used to securely expose your CRM deployment to the world.
WAP can do things that are out of reach of ARR, like preauthentication which is exactly what allows it to act as an ADFS proxy. On the other hand, ARR is smart when it comes to understanding http requests which allows it to do things like load-balancing.