go the 550 - the local garmin dealer in sydney talked my out of buying one due it was 1st gene - but also the bracket wasnt as strong or rugged as the 550!
I had a 550 which was very good indeed and used all over Europe. As my wife wanted to dump her totally useless Tomtom Rider, a new Garmin was called for so I got a 660 and gave her the 550 so I have good experience of both.
The first offering of the 660 may have been flawed with dodgy software but that is not the case now. Both 550 and 660 are very good satnav devices so the difference is in the detail.
- The wide screen on the 660 makes little difference as you normally travel from bottom to top and the extra width is used for soft buttons.
- The 3D buildings the 660 claims to have, I have never seen, and the lane warnings on junctions are limited and really just eye candy.
- The 660 locking on the bracket seems a little insecure at first but I have never had a problem with it and have never seen a post on this or any other forum by anyone who has. It is very fast to fit and remove compared with the 550 which can be awkward to line up on the bracket and getting rid of the 550's ludicrously stupid security screw is a must. I used both on Touratech brackets anyway as it gives a little more short term security when refueling etc.
-The 660 has a speaker so does not rely on a speaker in the car mount. This means it can play MP3 or act as a phone hands free without fitting it to a bracket. I have used it as a hands free for a phone by just leaving it on the passenger seat.
- The cabling for the bike mount is a lot neater on the 660. On the 550 you need separate power, mic and speaker cables from the mount (plus USB if you want an external antenna). The 660 uses a composite cable for everything which is long enough to reach the rear of the tank so individual connections are out of sight and out of the weather.
- The 550 is better with older mobile phones as it uses an earlier flavour of Bluetooth. I had problems with my Palm Centro with the 660 but my Blackberry Bold is perfect - even to the point of giving me voice dialling.
- The 550 uses a standard SD card which is easy to get to. The 660 uses a fiddly micro SD card which is a sod to get to. For me its no problem as its a fit and forget item. If you need to keep removing the card to swap MP3s or routes it could be a pain.
- When my 550 locked up on a trip in Italy I needed tools to get the battery off to reset it. The simpler battery on the 660 is the same as removing the battery on a mobile phone. Just unclip the cover and take it out.
- When I bought mine the 660 could be found cheaper than the 550.
- Although the 660 is wider, it is a lot slimmer than the 550 and easier to slide in a pocket when taken off the bike.
My conclusion is that when I bought the 660 there were some software issues that did not prevent it working but were a little annoying. Now it is great and, for my use, I made the right decision but I was also 100% happy with the 550.