Miles,
DMVPN for sure has this nice scalability factor which might be good for you.
VTI might also be a good idea, it's the stuff that gets a bit more traction in terms of supportability and new features coming.
I would base the actual solution on a few questions:
- Traffic volume
- Redundancy/Availability
- Support for protocols (will you need IPX, IPv6)
- Platforms you would like to deploy on (are there platforms witch very specific forwarding mechanisms - ASR, 6500/7600 with VPN SPA/VPNSM...)
- Third party devices support (?)
- Designated routing mechanism could be also of some importance.
(... probably a bunch of others...)
Marcin