I've tried pretty well most calls including several recorded calls and have never had a lot of luck with the latter. All calls will bring foxes in if they are really hungry but as already been said the Mark One Hand is probably still the best bet. WAM fox calls are pretty good if used properly, I've got a little fox whistle a mate brought back from Australia that works well too. Foxes are unpredictable and in these days of over lamping can be very difficult to bring in. As a matter of interest I was in a friends house last winter and his log burner smoked and the fire alarm went off, he opened the window and a fox was coming in at the gallop to the sound of the alarm!
I used the back of my hand for years, the windscreen with polystyrene, the small disc calls, similar to the sheep dog whistles, even a duck call on one or two occassions. another thing that is also useful are childrens squeaky toys, they also sometimes work for calling Roe bucks during the rut.
I also invested in a U Caller but the calls sound nothing like foxes in this country.
The only odd occasion that it has worked was because the fox was curious rather than thinking it was another fox!!