I can only speak for my experience with ordering custom (really MTM) from Santi. Since there wasn't a dealer anywhere near where I live, I had to have my partner do the measuring. The suit fit poorly at first, but Santi made changes to get it to a state where I'm satisfied. The biggest downside was the turnaround since it had to go all the way to Poland. I want to say it took about 2 months. I also was annoyed by the game of telephone between me, the dealer, the distributor and manufacturer regarding any communications on the adjustments to the suit. I imagine it would have been easier talking to DUI in San Diego instead.
If I had to make the decision again, I'd still go with Santi but just order an off the rack size. The loaner suit they gave me while mine was being fixed fit almost as well as the MTM but in different ways. I feel the quality of the Santi suit wrt to details like pocket design and boots is better and I also was really turned off by DUI's nickel and diming pricing for suit components that should be standard like pockets.