The Lakes tend to attract Tourists / Traffic, so I prefer the Mountains, nothing wrong with a night or two alongside a lake, but if you are after good riding research passes you can work into your trip and circular ride-outs you can do from a base (i.e. when stopping 2 or more nights at one Hotel)
Stelvio is a bit of a tourist trap too, on most people "Must Do" List but so much better in the area, The Gavia that runs south from the Stelvio is one of the most stunning passes in the Alps, The Albula, Fluella, Julier, Bernadino (and many more) are much better riding roads, and the Slugen is another stunning ride.
On your way through / back the Andermatt passes are also great, the Susten and Grimsel are two of the best (but it tends to be a choice of over the Grimsel and Furka OR over the Susten.
I think the Susten may just be the better pass, but if you have not ridden any of them before then Grimsel + Furka would win for me if the weather is good, two for the price of one ::008::
I think on your way down you will be a long way East if visiting Colditz - this will cost you a day in the Alps compared to a more direct route, and add a lot more dull roads into the mix, you can easily be in the Alps lunchtime on day two if going more directly (about 7 Hours riding from Calais to first pass) Colditz is a shade further from Calais, and then from Colditz to the Alps is another 5 hours riding.
Still 10 days is enough, especially if you can get to Colditz on the first day, wander around on day two, get close to Stelvio on day three, run over Stelvio (and Gavia) in day four on the way to Lake Como, have a few days here and back home in a 2 day blast.
I personally would stop in Livgo instead as there is more good riding in that area, or press back towards Andermatt to have a day or two riding around those passes - although now the Swiss Franc has gone mental you may be better trying a shade further south in Airolo to get Euro Prices not Swiss ones.
