I personally would never touch Photobox. They are dark and flat, their paper is not very nice, and their colours are not good.
It depends what you are using it for of course, and if its 'happy snaps' and bulk orders then Photobox are great for general service and price, as they are so cheap and quick.
But if you are looking for better results for something that looks more pro-am/pro or its a special occasion you are printing for, then there are some really good pro labs out there that would do a much better job for not much more money.
I would reccomend this company if you want a large bulk order pro results at cheaper price:
http://www.proamimaging.com/
And this company for quality:
http://www.loxleycolour.com
If I want a really special result, and for all my portrait/studio work, I use a fine art printer.
My tips to get a better result from every printer: - always choose satin matt/lustre finish, and invest in a screen calibrator/monitor calibrator, as you won't ever be able to get decent results without a callibrated screen.