Thought I'd replace my old Garmin 1490T. Picked up a Tom Tom yesterday just to see if they were any good. I have never used a GPS on a bike so I can't help you as far as mounting goes. But the Tom Tom will be returned tomorrow. The design and screen are nice, but thats where it stops. The lifetime map and traffic updates are worthless because they don't offer any on the website. Their website is messed up, and even if it did work it is more oriented towards Europe than the US. A single lane road near my house has been a dirt road for over 100 years, but shows as a two lane asphalt highway on the Tom Tom. Also it is a real pain to get to the most commonly used options.
Tom Tom jumped on the GPS bandwagon but can't provide. Rand McNally makes good maps, but has little experience in GPS also, they just rely on their name. I spent over a decade working with sub centimeter equipment as a surveyor so I know what does and doesn't make a good GPS unit. Magellan has some great units, but the price goes up. There are other GPS units that are killer, but the price is ridiculous for the average guy. When it comes to best bang for the buck based on the mfg's you listed, it's hard to beat a Garmin. Easy to navigate the most used features, and it's accurate