We have lived and cycled in San Diego, CA (16 years), Newport Beach, CA (3 years) , Los Angeles, CA (5 years), Washington, DC (7 years) and currently live in San Mateo, CA (3 years) (near SF Airport).
The best weather is San Diego and the best cycling is the Bay Area. Cycling in San Diego was great and in fact, we return quite often to cycle there. We recently spent a week cycling Newport Beach to La Jolla. When we lived in SD, we cycling the coast, the back country and Mexico. I never get tired of riding from Carlsbad to La Jolla along the coast.
The Bay Area offers much more diverse cycling including more mountains within easy access and we can ride from our house over Skyline (2000 foot ridge formed by the San Andreas Fault) to the ocean. The route goes through the redwoods and is very nice cycling. The tradeoff in the Bay Area is that it is very hilly. When we leave our house, we start climbing. Most of our rides are 75 feet of climbing per mile and can be more.
There are three major mountains - Diablo (12 mile climb), Hamilton (19 mile climb) and Tam (8 - 10 mile climb). Each mountain offers its unique challenge, reward and view.
The weather from April to November is low humidity, arid with little if any rain. The downside is the wind. We have a lot of wind which makes for some challenging riding at times but great sailing on the bay.
To the north is wine country and features interesting hilly terrain, hotter temperatures and wineries.
In general, the roads are okay to good with bike lanes. Some of the mountain roads are just that two lane roads with no shoulder.
Outside the US, we have cycled in Tuscany, Italy and Mallorca Spain. I really like cycling in Italy and Spain. Cycling is a real sport there and everyone cycles. The guy who drives the 18 wheeler's mother cycles. Motorists are very courteous to cyclists and likewise the cyclists I observed follow the rules. The Italians drive fast but it all seems to work. I do not know if we were any safer in Italy but it was a lot of fun cycling and hanging out with the Italians. The same was true in Spain.
As a footnote, cycling in Washington, DC, MD, VA was okay but the weather was too hot and humid for us. We prefer the drier arid cooler areas for cycling. We lived on the west side of LA in Brentwood. We did not do much cycling in LA but did a lot of in line skating in Santa Monica at the beach.
The Bay Area gets our vote as the best place to cycle in the US considering where we have lived . Abroad, it is definitely Tuscany and I could easily buy a villa and move there.
