The morph tool in Topogun is handy if you've made changes to the shapes in your reference mesh after you've done most of your retopology. You can then use it to reproject your new topology onto the altered reference mesh and everything should line up as they had before the change. I've done it a few times and it seems to work. 

 

ZRemesher is great - it's leagues above Qremesher in figuring out how a mesh should flow even without the guides. With the guides I find it does a decent job for the most part but the more guides you add, the easier it is for the feature to get confused oddly enough.