The hozelock one which screws down from the top is pretty good, although you need to be careful not to lose the different little black washers that are needed for different taps. You can get them from any DIY store.
Other than that, I have one of the ones which is like a big soft rubber thing with a jubilee clip round it that you tighten up, looks a bit like a clockwork key. That can fit a lot of different taps but leaks, put a bucket upside down over the top of it whilst unattended!
Also I carry a short little length of hose with a screw fitting on it like you have on an outside tap, just in case the customer has no hozelock fitting. you just unscrew theirs and replace with yours.
In addition to that, I have a hozelock double male spigot, so you can join hour hosepipe to the customer's. I also have a standard screw-together connector which can just join 2 pieces of bare hosepipe.
Since running my TM I've found with all of these I've never been unable to connect on to water
