It depends on the backroads – the road condition on some of them is pretty poor and there can be sections with poor visibility, blind corners, hedgerows and cars speeding. Had a few offs over the years with potholes or front tyres slipping due to unseen run off from the fields road a downhill corner.
However despite that i'd still say i prefer the back roads, one thing that is overlooked is how nice it is to breath in clean air when going at a good pace – busy a roads have all the problems with fumes and pollution and general road mankiness with grit, brake dust etc.