UK Flight Training and Rainbow air are different schools. One does FAA stuff (rainbow air) and the other does JAA training. They are run and owned by different people, although Rainbow Air is co-owned by a Brit. I've been to RA, and I would recommend them.
LA flying is good for the practice of flying in very busy airspace, but don't be fooled by the weather: the marine layer can make life very difficult for the VFR pilot: often visibility can fall to 2-3 nm, often in the mornings you can't see anything. I think the best time to go would be April time. I've been in Feb, and the weather was pants (raining all the time) and in November when the marine layer was still there. Very frustrating.
Personally, I think LA and Long beach is a dump, but its cheap living, and the flying is good. If you can cope with the basin airspace, you can fly anywhere in the world quite comfortably, your R/T will be greatly improved.