I've used Ridings regularly and can recommend them. Used Specsavers once but a slimy young sales person there persuaded me that I needed glasses with a non-reflective coating (about £30 extra) "because I worked with computer monitors". I found the glasses I received unpleasant to wear - the advice was absolute rubbish, but probably earned him a nice commission.
I stick with a local optician now because I trust them and it supports local business.