I'm going to go against the trend here and say Gaugemaster. There's a lot of models but my experience has been with a panel mount model UDS which is twin track with simulation and has been great.
Years ago I was looking at CDA, Gaugemaster and Morley to upgrade from two Hammant & Morgan Duette controllers. I've always wanted to try a controller with simulation/braking/inertia, all the same thing I believe, but favoured Gaugemaster over CDA purely due to knob versus slider. Morley have knobs too but they don't have simulation, which I hasten to add probably doesn't need it based on other people's comments on the web about it's slow speed performance. But I do enjoy using the simulator for its novelty in braking and accelerating slowly.
My only gripe is that I have on occasion had the throttle on around 75%, brake on full, then inadvertently switched the simulator off whilst reaching for the reverse switch. This sends the train off immediately at 75% throttle! I'm not a big fan of reverse switches and is why I nearly bought a Morley with it's centre-off knobs which is a feature I liked about the H&M Duettes. In the end the choice was simple when the Gaugemaster appeared second hand on ebay for under $100.
Back to your old Farish locos Gremlin, I don't know anything about their motors but maybe an old Duette might be the go? No I'm not trying to sell you one, I'm still quite fond of mine and doubt I'll part with them, but old locos, old controller - not real scientific I know. FWIW my Duettes were second hand, ancient, and bought over 10 years ago. They ran my Lima, Austrains and a Lloyds 30cl locos without issue and later TOR and Auscision for a short time before I got the Gaugemaster. The Duettes were a huge step up from the train set controllers I had. However, there's quite a few negative comments about their suitability for newer motors. There's a good link here which talks in depth about types of DC controllers and was the first time I saw anything negative about the Duette http://www.scottpages.net/ReviewOfControllers.html
I never chased up why the negativity until this thread popped up, but if you go to RMWeb there's a few good threads on controllers and explanations about what makes the Duette good or bad, plus comments about Morley v Gaugemaster.