does anyone know the easiest way to get from the paris/london eurostar destination in london to heathrow? thinking about taking chunnel back from paris in morning for an afternoon flight at heathrow....or am i better flying into heathrow?

Are you travelling before or after the switch from Waterloo to St. Pancras?

i believe st. pancras...did not even see the other choice when i was looking at my options...

You are better flying into Heathrow

Eurostar operations are changing from Waterloo to St Pancras on the 14th November. This makes it easier to get from Eurostar to several of the London airports. In your case the easiest would be Tube direct to Heathrow.

If you are short of time then taxi to Paddington & Heathrow Express would be a substantially more expensive option that would save 20 minutes or so.

BUT why do you want to arrive in the UK on the day of your flight - what happens if something goes wrong and you end up stuck in Paris when you should be at Heathrow

Have you considered an open-jaw ticket so you can return home from Paris?

The tube takes 60 minutes. Allow at least another 30 for getting to the tube platform at St Pancras, waiting, and getting from the tube at Heathrow to the checkin desk. Procedures at St Pancras aren't yet fully announced, but even though you go through UK immigration in Paris, the passport control desks at Waterloo are sometimes manned, and non-Europeans might have an added delay on arrival at St Pancras.

Given that this is about the most boring train journey in the world (the Channel Tunnel is just a tunnel: there's nothing to see), I really can't see the point of taking such a convoluted route from central Paris to Heathrow. Simply get a taxi to CDG and a plane.

We are traveling between the London area and the Continent on a near weekly basis (to Brussels, instead of Paris).
Flying is probably the best bet, but check fares anyway. It's easier and may cost about the same. There are only two basic reasons we'd recommend Eurostar over flying:
1. You've never ridden Eurostar before and you want to try it just to satisfy your curiousity. That's a perfectly legitimate reason and it doesn't matter whether the route is more or less exciting or more or less expensive than flying.
2. You're traveling late November to mid December and your flight from CDG isn't "linked" to your flight from LHR. IOW, if your flight to LHR is delayed or canceled, how will that affect your flight from LHR? If you can be rebooked onto another plane at minimal or no extra charge, then fly. BUT...heavy fog problems aren't unknown at that time of year. If a delayed or canceled flight from CDG means you'd have to buy a whole new ticket from LHR, then consider the train...it's (somewhat) more reliable in dodgy weather than flying. But you'd have to catch an early train and plan for the palaver of getting from St. Pancras to Heatrow...options include a variety of mass transit possibilities (the Tube to Heathrow would probably be easiest if you don't have a lot of luggage) or even a car service.

FYI, *IF* you opt to take Eurostar, keep your ticket handy when you get off in London. Even if there isn't a full blown immigration line, occasionally they do spot checks asking to see your ticket. It only takes a second, except for pax caught unaware who've stuffed their tickets away somewhere and have to drop everything to dig them out again.

Generally, though AlanRow is right...you should consider coming to London the day before your flight, will be much less stressful.

Even though Eurostar and flights are both quite frequent, I wouldn't do either one the day of my flight. I would not want the hassle of checking out of my Paris hotel, getting to Gare du Nord or CDG, traveling to either St Pancras or LHR, and out to LHR (if you take the train)

Just too much can go wrong and the penalty for missing your flight is very high.

I'd personally take the Eurostar to London the morning before and have a day/night/morning in London. But if you have no interest in London, then I'd fly to LHR the evening before and stay at an airport hotel.