I asked Mr. Niazi in Cisco this question again and received the following answer:
Here are the recommended versions now:
OS 12.4 Mainline: 12.4(3c), 12.4(5a), 12.4(7)*
IOS 12.4 T-train: 12.4(2)T4, 12.4(4)T
In general we run 12.3 or 12.4 Mainline on DMVPN hubs and 12.3T or 12.4T on DMVPN spokes, but this is not a strict rule at all.
* 12.4(7) is particularly good on the DMVPN hub routers when using EIGRP as the routing protocol, a number of EIGRP fixes/features were added that makes EIGRP more stable on DMVPN networks.
The usual disclaimer goes with the recommendation: the images have proven to be stable in our internal test and beta networks as well as most of the customer networks. Since every customer environemnt is unique, you might (a remote possibility) find some corner-case type issues in your network.