All the answers are good. Sometimes the area can be quite foggy and other times really nice. If you really want sunshine you need to be in Potrero Hill, South Beach/Mission Bay/Central Waterfront and The Mission. I grew up in Presidio Heights and had friends all over the City. I can tell you there is fog everywhere. Some areas have fog in the morning and it usually burns off by noon. Other areas closer to the ocean have a lot more fog.
Cole Street is more laid-back than Union, Chestnut and Fillmore Streets. There are most restaurants and shops in other areas of the City. But the ones in Cole Valley are good!
Jed is correct in that there are more homeless around the area. Parking is also a negative but then, parking is tough in most neighborhoods. Go to www.sfgov.org to check out police reports for crime stats for all the areas of San Francisco.
You can go to my website for a description of all the different areas as well as advice on buying property. You just need to decide what is important to you and go from there.