Home Base for England

Just from my mental map of central southern England I'd say the most central location from which to visit all of those places is either Salisbury or Oxford, with Oxford certainly offering the best road and rail connections to most of them. How many days do you want to spend in London? It's the most easterly of those towns and cities and the most expensive to travel to and from, as well as the most expensive for accommodation.

We've used London as a base many times. You can reach Bath, Stratford-upon-Avon, Windsor and Oxford easily by train. I don't know about Salisbury. For the Cotswold area, you can do 1/2 day trips from Stratford-upon-Avon or Bath. But for 10 days, that's ALOT of day trips. I'd suggest you narrow things down a bit. Definitely include Windsor. And probably Bath. Then pick one more. You might find this article I originally wrote for AAA Carolina's 'Go!' magazine helpful. I've modified it and posted it on TripAdvisor.
http://www.tripadvisor.com/Travel-g186338-c176673/London:United-Kingdom:London.And.Day.Trips.html

Why not split your stays between Salisbury or Winchester, somewhere around Stratford, and London? There's no reason to stay in the same location all the time unless you are renting an apartment at a really good rate. It's fun to explore different locations in the evening instead of spending too much time retracing your steps to London or some other "home base."

Hey, Thanks everyone! All of these are great ideas. Our current plan (the one we've been going with for the last two months) is to stay in Bath and see Salisbury from there, then Stow-on-the-Wold and see the Cotswold region and Stratford from there by car, return the car to Bath and take a train to London and take at least one day trip to Windsor from there. The remaining days spent seeing some of London. I agree that is way too many day trips back and forth from one location. Thanks for all the good advise!
Chris

You might save a bit of time and money if you kept your car for your trip to Windsor, then turned in the car at Heathrow. We have returned cars there - it isn't complicated driving, since the car return is on the western side of the airport complex.

Thanks Cynthia. That sounds like a good plan.
Chris

The train from Paddington to Windsor is only about 8 gbp. I'd certainly not hang onto the car to save that. The train from Bath to London is about 38 gbp or cheaper if bought early (from memory). You can get the right rental car and leave Bath early, drop the car off in Slough and then see Windsor. The problem with that is there isn't any baggage storage that I'm aware of. Bath is a very expensive place to stay versus the surrounding towns. I also think 1 full day in Bath is plenty for the major sites. You can easily stay in Wells for much less and you are close to Bath and Glastonbury (but in opposite directions). There is actually good bus service between Wells and Bath because the last thing you need/want in Bath is a car. Salisbury is an easy drive away with many attractions in between. This is a good area to have one or two day stays so you don't spend a lot of time back tracking. You'll save a lot of time and money doing this. A car would work best for this trip. You can see a lot of it by train, bus and tour but a car will make many sites available that would otherwise be difficult to see. Without a car in the Cotswolds, you will be almost totally isolated. You will be able to get around but you will not spend your time efficiently.