Well to throw in my two bits here: my first suggestion from a usability standpoint would be 3xLogic Vigil... since I'm extremely familiar with it and I think it would fit all your criteria, including being easily configured by an on-site tech, and offering great central management with a fully-featured Windows client app that can show cameras from multiple sites all together, and the "RapidStream" feature would be handy if you're monitoring multiple sites over WAN.
It also doesn't tie specific cameras to a license, so if you bought, say, a 16-channel Hybrid system, you could plop that in any site and connect and combination of any brands of new or old IP and analog cameras, and be off to the races.
The downside is, it's not a cheap system. Not HORRENDOUSLY expensive either, but not cheap.
My other suggestion - and it may not be a popular one - would be Dahua-made (and sold under various other names outside China) DVRs, NVRs, or hybrids... again, extensive remote management, and viewing and playback of multiple sites using both main and sub-streams via the PSS client, direct configuration of both recorders and Dahua camera from PSS, which gives you the ability to connect to cameras directly from the same interface on small sites where you may only need one or two cameras and don't require a recorder.
If you use one of the NVRs with built-in PoE, cameras plugged into them will automatically grab an IP from the internal DHCP server (assuming the cameras are set for DHCP), and the system will find and add all Dahua and most ONVIF cameras with a couple of clicks - just click Search, click Select All, click Add, and you're done. Or drop the recorder on site, give it an internet connection (recorders support UPnP), plug in your cameras, give the WAN IP to the person on the remote site, and walk away - it can all be configured from PSS.
Best part is, it's a reliable yet extremely cost-effective setup and if something gets broken (being moved around to various environments, including outdoor), it won't cost a fortune to replace. And again, no per-camera license fees, and certain no tying of camera licenses to specific cameras.
Downside is, it's not the most user-friendly interface, with a lot of Engrish, BUT... once you're familiar with it, it's not bad to work with, and the configuration is pretty consistent across all the recorders and cameras.