Need Help Westminster area to Heathrow

Depends on what you mean by best. I would think that best to having your own driver. If it was us, we would take the tube. You have lots of time.

Tube is fine.
I am not quite sure where to go.
Does the Tube go all the way to Heathrow?
I read something about a Heathrow Express.

thanks

Of course, it goes all the way and then some. Depending on your stating point you may have to change but it is easy. The H Express runs direct from the Paddington station but it a lot more expensive and you would have to get to the Paddington via taxi or tube. It would be at least an hour on the tube. Ask you hotel for the closest tube entrance.

Your hotel is right next to St James Park station. District or Circle line to South Kensington, transfer to Picadilly line all the way to Heathrow. I always take the Tube to Heathrow.

thanks for the info.
Does the Tube have a pass that can be used like the 5 day pass in Paris that has unlimited rides?

Slight correction. From St James Park station, take the district line to Hammersmith, and change there to the Piccadilly line to your correct terminal.
In both cases check the indicators, as the routes split and you need a train going in the correct direction. Heathrow has different stations for different terminals, you need to check the train is going to your terminal.
The difference is at Hammersmith, the District and Piccadilly lines are on the opposite side of the same platform - easy. At South Kensington they are on different levels. Escalators and stairs are required.

See the tube map here: http://content.tfl.gov.uk/standard-tube-map.pdf

Does the Tube have a pass that can be used like the 5 day pass in Paris that has unlimited rides?

What you need is an Oyster Card. This is like an electronic purse. You buy it (£5 at any tube station), and load it with money (at any tube station and some shops). Every time you enter or exit a tube station, or get on a bus, you hold this up against a reader and the gate opens. With practice you can do this without stopping (like a good Londoner).
The advantages are that Oyster tube fares are half what you buy for normal fares, you can no longer by bus tickets from the driver, and when you reach the price of a daily pass, it stops charging you, everything after that is free for the rest of the day. So you don't have to work out in advance if a pass will pay off, the daily cost is "capped".
You can also use some contactless credit/debit cards and don't even have to buy an Oyster Card.

I agree with Chris.....District to Hammersmith, change to Piccadilly line (make sure the train is going to your terminal. And some PIccadilly trains don't go to Heathrow at all.)

Figure about an hour for the ride.

If you get an Oyster card, you can turn it in when you get to Heathrow and get a refund for the 5 GBP you paid for the card as well as any remaining money on it.

You could take the Heathrow Express but it really wouldn't save much time as you still havae to get to Paddington station but cost you about $25 per person more in fares.

Lastly, you could enquire about a private car service to Heathrow ( usually shared.) Your hotel can help with this. I know from my hotel in Earls Court to Heathrow with one bag it's 44 GBP. (I have never taken it as I take the tube.)

I'd actually transfer from the District Line to the Piccadilly LIne at Barons Court, it's a small station so you just wait on the other side of the platform.

We have booked with BA Transfer in the past and have had great success. They provide a private car and take you door to door. They will be waiting for you at Heathrow in the Arrival Hall. Their drivers are very professional. You can book on line from the US before you go, as we have done. Take a look at their website and their rates to see if it is something you would consider. We are traveling to London in about 10 days and have already booked with BA Transfer to take us from Heathrow to the Pimlico area (not far from Westminster) and later back to Heathrow. We think they're a good value.

I just looked up BA Transfer ( https://www.batransfer.com ). Heathrow to Westminster: £42.
Using the tube (with an Oyster card): Peak : £5.10 (Monday to Friday from 0630 to 0930), Off Peak: £3.10 (At all other times including public holidays.)
It's your money, you choose.

When taking the tube, ensure you know which terminal your flight departs from, so you get off at the correct stop. There are a couple Heathrow stops. From St. James Park, there are a few stations where you can transfer to the Piccadilly line, South Kensington, Gloucester, Earl’s Court, Baron’s Court, Hammersmith, etc. When transferring lines, make sure you catch the train heading to Heathrow and not Ealing Broadway.