Paddington station to King's Cross station with luggage - taxi or the tube?

tube at non peak hours - non rush hour - but during rush hour TAXI

It is very easy - no need to change Take a westbound Circle (Yellow) or Hammersmith and City Line (as it is now called - Pink) from Kings X - St Pancras to Paddington. Nowadays that puts you at the far end of the station rather than Praed Street, but that's progress for you. As others have said - unless you are in a hurry, you can get the Westbound Piccadilly Line (Dark Blue) all the way to Heathrow - not much slower than faffing about changing at Paddington - and takes you right into Terminal 5 (Be sure to get the Heathrow 1,2,3 and 5 service). This is the way I always go - and it takes about an hour depending on the time of day. The London Tube system is world -famous for its clarity of signage so it is quite difficult to get lost.

Taxi possibly better but of course more expensive.

Paddington and Kings X both on Circle/Met line so big cars, no escalators and more space so shouldn't be too difficult. (Depends on what time you're doing this, though; I wouldn't try this at 8.30 on Tuesday morning!)

TAXI all the time, i cant stand the tube when carrying any luggage, its too much stress...

taking the tube would be pretty easy, but i always take a cab, i find it more relaxing and no stairs or esculators

I'd hail a black cab or catch the circle, metropolitan or Hammersmith & City line.