tour group recommendation to London/Paris from Los Angeles.?

Is there some particular reason you are interested in a tour group?

I have no use for group tours to anywhere but London and Paris are so accessible to an American tourist (as opposed to traveling to Kazakhstan for example) I'm not sure why anyone would need a tour group.

You don't really need to join a tour to see London and Paris. Both cities are relatively safe and easy to get around when traveling alone. Just plan out things you want to do and places you want to see in advance, figure out transportation, and you should be fine. The public transportation system in both cities are user-friendly and you can get around pretty easily.

A major drawback in joining a tour group is time limitation. You will be rush to move onto the next destination all the time. Plan your own trip and be your own boss. Remember, it's YOUR vacation and YOUR time.