UKH

Who's good for doing mid sized (maybe 12"x18") prints these days?  I've not had any made for some time now.  Quality is a priority over price.

And is it still a good idea to do all my own colour balance, sharpening, etc, or am I better off just giving them the raw file and letting them do all the thinking?

https://www.amimage.co.uk/

Cheers, I'll take a look.

White wall seem to be very good so far.. https://uk.whitewall.com/ very true to the image i send. I've only used their "Photo" printing though (up to 40"x60") and tend to go for the higher end photo papers. I'm tempted with a metal or acrylic print, but waiting till I get the right image

I've had multiple issues with photobox seemingly reducing exposure levels (to be fair they've always sent good no-quible replacements in a matter of days) but i can't find anyone else that prints on poster mount board (which I like) so I still use them for some stuff (e.g. local photo comp displays)

I've recently got some framed prints (about 60cm by 40 cm) from https://www.picturegalleryuk.com/   
The quality seems brilliant to me and I'm really happy with the results. Their website is really easy to use the service is great. A friend recommended them.