Garmin Zumo 340LM for me. It's beautifully made, waterproof and has lifetime map updates. The audio instructions are quite loud but you'll still need an earphone of some sort (plug-in or bluetooth) in the 3 Wheeler.
It uses RAM based mounting hardware which is first rate. Quite a consideration if you have a 3 Wheeler!
I have to admit that I don't find the Zumo as intuitive as my old TomTom but it's not too bad once you get used to it.
It comes with a power lead (incorporating a 5 volt step-down circuit) designed to be hard-wired into the bike wiring harness. I have attached an regular accessory plug to this so that it can be easily moved from vehicle to vehicle. [I have also obtained a suction type ball mount with a massive 3" sucker for the tin-top's windscreen.]
I'm just getting to grips with the BaseCamp route planning software which seems very powerful. There are several useful tutorials on YouTube to help with this.
They are pretty pricey - I got a 'refurbished' one off eBay which is effectively brand new but without the retail packaging. If your budget can stretch to the Zumo 390LM it has a 'Curvy Road' feature that can default to twisty (i.e. good driving) roads wherever possible.
Great idea but quite pricey...
