I love Splash for shallac manicures. It's so easy to get an appointment and the manicures are always very well done. I accidentally cut the shellac on one finger and they were able to see me immediately the next day and re-did it free of charge.
I've been going to the Goodge St salon for beauty treatments for 3 years and the manicures (even express-OPI) always last really well. Such good value for money.