Here's my problem with the Sonoma Mission Inn...while it is a great property, the area immediatly outside the gate is not very pretty....gas stations, warehouse etc...This may not bother some people, but I find it annoying especially when I come to wine country expecting something else. Again, the place itself is very nice as is the spa.
Can't comment on the other two places although the Kenwood Inn has always looked very nice. You could also consider McArthur Place which is nice and you can walk to the town square with all the shops and restaurants.
You could also consider staying in the town of Healdsburg which is still in Sonoma County. There is the Healdsburg Hotel, Mars Hotel and tons of other places including nice B&Bs and inns.This is my favorite town in the area with lots of great shops, cafes and wineriers. Plan to stop here for lunch on your travels.