I went though the same debate at the start of summer. I ended up with the Sony HDR-AS15 which had the quality I wanted at a price way below new GoPro’s. Amazon where knocking them out for £170 due to the new model coming out.
I’ve seen lots of people talk about mounting being a problem, but there is an easy way of using all the GoPro mounts buy using a Veho tripod mount adaptor, if you do a search/look at my other posts you will find a video on how to do this.
I’ve used the Sony at the FoD and in the Alps mounted on a chesty, rear facing on the seatpost and mounted on the handle bars on a family ride.
The footage is great for reminding you of good days out on the trail, but insanely boring for anyone who wasn’t there unless you are good at editing….I’ve not had the time to make mine interesting.
Anyway, in summary…Sony slightly better than a GoPro Silver, can easily use all the GoPro mounts with the purchase of a £10 bracket, cheaper to buy, has a phone app for viewing etc.