I have to go to Cambridge next week and need some help regarding the transfer possibilties...Train via Kings Cross, Bus. What is fastest and cheapest way?

Also faster and cheaper than Heathrow Express - Kings X - Cambridge

Frequent service, details on http://www.nationalexpress.com/

Bus would be best. Does take some time since it stops everywhere.

See link.

Thanks a lot for your answers! And what about London City airport?

Stansted is, by far, easier to reach Cambridge than Heathrow, Gatwick, or London City.

I did this several times over the summer. I flew SFO-LHR both times.

Trip 1 Heathrow Express to Paddington, Hammersmith and City line to Kings Cross, train to Cambridge.

Advantages:Heathrow Xpress train is really fast.
Disadvantages: Train is expensive, you have to lug luggage up and down stairs at Paddington (actually I don't recommend taking Hammersmith and city line because it is far away from the other tube lines at Paddington, it's easier to take the circle or other line). And I think that the time you save taking the Heathrow Express is eaten up by taking the tube between Paddington and Kings Cross.

Trip 2 Tube from LHR to Kings Cross, train to Cambridge.

The tube takes about an hour, but you only have to get on and off once. And because you are getting on the tube at the airport, you will probably find a seat for you and your luggage. It's also cheaper to take the tube than the Heathrow Express.

Expect to spend about 16 GPB for a one way ticket b/ween London and Cambridge.

LCY is fairly easy - just get the shuttle bus to Liverpool St, and you can get a (slower than King's Cross, but not bad) train from there.

But, as said before, STN is by far the best airport for Cambridge. There are direct trains and coaches, and it's only about 30 miles away. Assuming you're coming from Germany (given your profile), you should be able to get a decent Air Berlin flight into STN. It's really a lot less hassle.

Thanks for all your help!!!
I have to fly LH to LHR this time but will take Germanwings from STR to Stansted the next times. Much cheaper than LH/BA and less hassle to get to Cambridge...Paid just around 50 Euros return for my next trips.

I imagine it is frequently faster to take the Tube from Liverpool Street to King's Cross than to take the slow line up from LST. When I come with a lot of baggage, however, I prefer to just take it from Liverpool Street.

Also, the shuttle bus from LCY to Liverpool Street costs �6!

I wouldn't bother with the Heathrow Express. It is a waste of money if you are going to have to transfer via tube afterwards.