For me, the benefits of using true ECN/STP over an MM/DD model are clear, especially at the present day when execution with an ECN is pretty much instantaneous with no re-quotes and you can always get filled unless you're placing an outrageous ticket size.
Does anyone actually use/prefer a DD...
Regulation is very important Peter! I would not recommend signing up with an unregulated broker in any circumstance, no matter how attractive any sign-up offers may seem. Protecting your capital at the source should be your biggest priority.
I think it really depends what you're looking for. Tighter spreads on ECN but instant execution on MM/DD. However, like a lot of people have said here, execution on most modern ECN platforms is pretty much instant with no re-quotes.
A lot of traders like the 'peace of mind' factor that comes...