need help for London

Neither, Driving into London is a disaster, and you are likely to hit "congestion zone" charges. And staying near Heathrow and commuting in is a bad idea.
Dump the car at Heathrow or somewhere else on the outskirts of London, and take a train in. Stay two nights (1st and 2nd July) in a hotel in central London and visit everywhere you want to see. Then, on 3rd July take a train (Heathrow Express or Piccadilly Line, depending on hotel location and budget) out to Heathrow (assuming your flights are from Heathrow).

Too many reasons why driving into London to see Tower Bridge and the Globe is a BAD idea. Don't even consider it.

Return the car to the airport.

Train, bus, car hire, or tube from Heathrow into London. Arrange an accommodation in London so you can spend a few days exploring, then take the tube or Heathrow Express or Connect train or a car service back to Heathrow on the 3rd for your flight home.

Could you drive to Oxford and return your car there? Spend the afternoon of the 1st in Oxford, before an evening train to London Paddington. If you book accommodation near the station you will be handy for the Heathrow Express as well.

As others have said,it's pretty much impossible to drive in London.

Heed the advice of others here. Sometimes I chuckle to myself. I remember the National Lampoons Vacation movies. The first one where they drive past the Grand Canyon and they get out of the car and take a quick peak and move on. And then the European one where they get lost on the roundabout in London or their other misadventures as they travel through Europe.

Thank you everyone for your advice...and after reading the comments my daughter & I agree and will have to make a decision soon! We are so excited to be visiting England--my dream!