Is the plan for one DC to take over for the other and vice versa? I don't think neverfail would do that. XO has some great tools for the exchange side and depending on the setup for storage EMC does as well. This isn't a simple do this and your all .. you need to figure out your timeline when things will be available and how the DC's / AD will swing over etc. Currently we need something like 50tb to replicate.
We just did our yearly test and we had exchange up and running in hour 6, BES was available 30 mins after exchange was online.
This really depends on what the business needs and to a greater degree .. what they want to spend .. $$$