UPB
I'm surprised I didn't see it on this list. It is powerline but boasts 99%+ reliability. I have played with it and it seems as solid as it claims. It is significantly more expensive though ($75 for a switch) so that must be considered. However when it comes to HA I like it's reliability and instant response.
I have no experience with Insteon but hear good things. I have minor experience with Z-wave. Just used the Intermatic USB stick and 2 devices. I had problems maintaining solid connections. Obviously 2 devices provide a weak network and Z-wave gets better as it grows but it wasn't a good start.
Looks like Misterhouse has a UPB driver. It is written in Perl and can run on Linux so I have no idea if the driver can be ported/hacked/used with LMCE. Misterhouse is Open Source so they'll probably be helpful.
http://misterhouse.wikispaces.com/UPBIf UPB is working with LMCE, it will be incredibly solid.