Ask your wife which lake she prefers, perhaps?
Where you are staying in the Dolomites, as that might well dictate which lake you visit for (it seems) a day.
Yes, they are a popular destination, but you are going ‘in a few weeks’ by when the main holiday period will be over.
I wouldn’t worry too much about avalanches, any more than I’d worry about packs of wolves.
Yes, like most roads along coasts or edges of lakes, they are constricted, not least as one side requires swimming trunks or (preferably) a boat. There again, the lakes are nice to visit and, I guess, iconic. You can have more than your fill of ‘Great roads and hooning, mate’ in the Dolomites themselves.
If you are going for the day, you presumably don’t need a hotel.
All that aside, Lake Como is often described as the nicest of the lakes.