choose siemens over bosch if its fully integrated, as most of them are currrently working out at about £30-50 more than an equiv spec decent bosch, but with a 5 yr p&l warranty, instead of bosch and miele's 2...
also mind, im a bit biased - personally never liked miele dws, they are expensive, and solid, qand the old ones did go on forever, but many built since the millenium have since died, not cos they were irrepairable, but just because they were uneconomical to do so. this is because parts are also expensive. so im just not convinced its worth the initial outlay on them. apart from anything, £56 for a drainage waste hose is jawdropping... im also not convinced they actually wash as well as bosch/neff/siemens stock either.
which? are always choosing bosch or miele as best brands, so theres no difference there, and majority of best buys year on year in dw categories tend to be bosch/neff/siemens usually with the winner dependant on which offered the best value for money at the time of testing.
best thing to do is order brochures for all 4, work out which features you find particularly necessary (half load for instance if your usage is not often every day) and which features you would feel are of occasional use. make a short list of those that you are after and then hit your local independant with the homework you have done.
its also worth noting siemens and bosch have released extra tall models that allow for particulrly wide diameter plates to be adequately cleaned in the dishwasher. both top line bsh group and miele also offer 3 tier drawer systems which open up the room on the bottom basket for more place setting by using a third shallow top shelf for cutlery instead of a cutlery basket
some people love this arrangement, others who like to remove and fill the cutlery basket from the sink, because the dw is not within arms reach hate it. its all about layout of the kitchen in that respect.
hope that helps!?