I had a suit made for a wedding by King and Allen. Others have said they didn't rate them, but mine came out very nicely after 3 fittings.
That said - I lost a load of weight this year and so it hung off me like a sack. I called K&A who frankly weren't that helpful, suggesting that a major alteration wouldn't be easy, would be costly, etc. - IMHO trying to convince me to not bother / get a new one, which I don't have the budget for. Maybe they're too busy with new makes, whatever, I didn't feel 'valued'. So I took it to a local tailor in Guildford who couldn't have been more helpful, who resculpted the jacket and 2 pairs of trousers for less than the cheapest suit I could find on the high street - well under £100 - and it now looks fantastic.
So as well as some K&A feedback - a bit ying and yang there - my next 'tailored' suit will almost certainly be an off the peg quality one from one of the better high st chains (probably in the NY sales), and then whipped down to be fitted for me. Which would be my advice unless you're a really odd shape.