I originally had a Rider and suffered from the common bracket failure coupled with Tomtom's aweful service. I bought a Garmin 2720 as I needed a working satnav quicker than Tomtom could fix the Rider. I now have a Rider Mark 2 as well as a replaced Mark 1 (free gift, eventually, from Tomtom after I complained to big boss). I also have an HP Ipaq which has a built in gps and Tomtom Navigator software.
I don't have experience of the Zumo but as a comparison between Tomtom and Garmin, to me, it's a no brainer. Garmin every time.
The Rider Mark 2 bracket is a massive improvement as is the supplied RAM mount. I am not sure about the change from the Bluetooth dongle to the Cardo headset though. I found it a sod to fit on a helmet. My BMW System 5, Schueberth C2 and wife's BMW System 4 all needed slots cut in the neck skirt to fit it and it's a pain having to remember to fiddle the microphone up under the helmet (before putting gloves on) every time. Also it's the base model supplied so if you need rider/pillion comms it's no good.
As Tomtom have still failed to include an audio out socket Bluetooth is the only way to get sound out so if you use an Autocom, etc. you throw away the £80 Cardo and spend £80 on another Bluetooth dongle.
If you need to use the Rider in a car as well the Rider 2 car bracket is much better than the Mark 1 as it includes a speaker. Unfortunately they designed the arm on the suction mount too short so its a bugger to clip the satnav on if the car has a sloping screen (99% of cars).
If you travel in Europe the Garmin European mapping covers more countries than that supplied with the Rider. Tomtom have nothing to compete with Mapsource and I find Garmin software much more intuitive to use.
My experience of back up service is for Tomtom to take eight weeks to replace the original Rider and Garmin replaced a 2720 which I damaged (my fault) by return of post and free of charge.
Nothing to choose between them on speed camera alerts. I use pocketGPS on the Garmin and have used them on the Tomtom 1. As Tomtom gave us a free subscription to their's on the Mark 2 we use those for now. If you use PocketGPS files they are easier to install on the Garmin (using POI Loader software) than they are on the Tomtom which requires the files to be copied across on the computer, then the alert distances and tones set up manually on each one.
If you want traffic info the Garmin is much better (not so useful on a bike but can be in a car). A one off price to buy the adaptor gives me constantly updated info on the Garmin. The Tomtom system requires a subscription (again we have a free one) and requires a data call via mobile phone every time you want the alerts updated. I found it a sod to set up my phone to work with this and it took about six calls to Vodaphone to get it to work.
The installed POIs are pretty good on both but there are many more on the web for Tomtom than Garmin. Never found a lot of use for these though apart brom BMW dealers. Do I really need a list of Ikeas or B&Q Warehouse on my satnav!
In clear conditions the Garmin gets a fix quicker but the Tomtom will hold a fix better in poor conditions. Maybe the more recent Zumo is better here. In practice I have no problems with either. We have set them both to find the same destination and there are sometimes minor differences in routing but both are sensible. One potential problem with the Garmin is that it's possible to "tweak" routing preferences. Sounds good but it invariably seems better to work with defaults.
The Rider 2 gets used on my wife's bike and car occasionally, the Garmin is used all the time and has proved itself all over Europe. I don't think the 'extras' on the Zumo are worth changing from the 2720 but if I was considering changing it would definately be a Garmin again.
not once has it taken me off at a motorway off-slip only to take me back down the on-slip and back on the motorway!
Intersting that a Zumo did this. My 2720 never has!
I'm sure if you wanted to spent weeks on you're PC (not Mac as the software isn't supported) planing a route across europe and taking a laptop with you to upload routes.
This is one area I have found vastly better on the Garmin. I don't know where "weeks on a PC" come in but when we wanted to plan an eight country trip around Europe the Garmin Mapsource software was great. Click on waypoints on the map, make them into a route (couple of clicks), transfer the route to the Garmin (two clicks), job done. Try doing this on a Tomtom, it's a long frustrating job doing it on the little touch screen. It was so easy that I bought a small Philips Freevents laptop that would fit in the top box and we found planning from hotel rooms to be very quick and easy.