I moved to Atascadero 2.5 years ago after looking at all the areas you mentioned. I likeed Atascadero due to San Luis Obispo, Templeton, and Paso Robles all being approximately 10-15 minutes away.
Atascadero is a very rural, bedroom communtiy, with no traffic problems.
Although there are no large stores in the town, with the exception of The Home Depot, we just head to Paso or San Luis to go shopping.
Homes in Templeton on larger lots and in nice areas are expensive, whereas Paso has a lot of homes on acreage at a great price.
I did not buy in Paso is due to all the growth over the years. It has become very busy, lots of new homes and stores, and when the market rebounds, will grow even more. That did not interest me and I wanted to stay in a small town.
There are a lot of nice restaurants and stores in Paso, and it offers a lot of diversity . Personally I would prefer to take the 15 minute drive and have the best of both worlds in Atascadero. It all depends on what you are looking for. A smaller town that does not offer the amenities Paso does, or a town that has a lot of growth. There are a lot of foreclosure properties in Paso, yet a lot of them are not in town, but located a few miles out of town or towards Lake Naciamento.
There are a lot of foreclosures in Atascadero too, but they are in most part, condo's and residential homes. There are some homes on acreage yet they tend to be on the outskirts of the town which may appeal to you.
I am currently looking for a home in Arroyo Grande and have not listed my home yet. It is 2,360 feet, very well built, in 2003, 3 bedroom, 2.5 baths a large office,three car garage, on 3.25 acres with plenty of room for a pool. It is located at the end of a half mile private paved road, so there is nottraffic, and an electric security gate for even more privacy. Due to the location and all the privacy, I never lock my doors or take the keys out of my cars, even while on vacation. The propery is fenced and cross fenced to keep the deer from eating my landscaping, and two plus acres of fenced areas for livestock, and it also gives a lot room between homes. All the homes are on at least 3 acres, some on more, it is very quiet, literally 3 minutes to the freeway on/off ramps, and 10 minutes to the grocery stores and less to get to town. Although all these are so close, it is very rural and one would never know these ammenities are so close.
If you would be interested in knowing more, please let me know!
Good luck in your decision....it is not an easy one!