Horses for Courses is dead right. Personally I prefer the RealDrive on the Zimo precisely because it is not too throttle responsive, it has huge inertia settings and accelerates and breaks slowly in a very prototypical manner. However some folk do not like this and prefer the more direct throttle response of the LokSound 4.0 decoders (i.e. before the recent addition of 'Full Throttle' drive).
I too have both and like both, but I nearly drool when driving the Zimo with real drive. I love the way heavy trains labour out of a station with the GM thrashing and notching up and down automatically in a very realistic manner. F5 puts it in light train mode which makes it more throttle responsive like the LokSound 4.0.
Now I have not yet driven the new LokSound 'Full Throttle' decoders which seem a huge improvement in terms of prototypical drive and sound, and possibly an improvement on the Zimo. I can't wait to get one and try it, I really like the sound of their new features 'Drive Hold', 'Coast','Brake','Dynamic Brake' and 'Run 8'. Will report back a comparison with the Zimo once I get my hands on a 'Full Throttle' decoder.
http://www.esu.eu/en/products/loksound/loksound-full-throttle-features/