Generally older models without a dpf (pre-2009) and those with a Bosch injection system give the best results. Vehicles with a Siemens or Delphi system won't usually give as large a bhp increase (ie above 3000rpm), though the results below this can be almost as good as a Bosch system.
So if you asked me which used vehicle to choose I would say a pre 2009 Alfa, BMW, Chrysler, Fiat, Hyundai, Jeep, Kia, Mercedes, Renault (not 1.5dci) Saab, Vauxhall, Volvo 2.4d.
Some engines have a fuel pressure limiting valve fitted to the fuel rail or injection pump which prevents the maximum fuel pressure being raised by much so the bhp increase above 3000 rpm is restricted. Examples are: Honda, Mitsubishi, some Nissans, Subaru, Toyotas, some 1.7L Vauxhalls and others with a Denso injection system.