Count me as a bit of a contrarian here.

I would previously have said yes for pre-clearance alone, ignoring the TPs. However my experience of US immigration in the US (not at JFK as I've taken the LCY flight there recently) in the past few months has been significantly better than it has been for years. The new kiosks ( http://www.cbp.gov/travel/us-citizen...rt-control-apc ) seem to make it much much quicker for the average person, which in turn means much shorter queues.

They also seem to have focused on improving the image that their immigration system projects to visitors - so e.g. the tone of questioning I've had on entry from CBP officers is now significantly "friendlier" than it used to be and I have seen people carrying out surveys post-immigration asking about experience, how its changed, and whether it makes one feel positively inclined towards the country and happy to visit.

I will likely book via LHR in future if this turns out to be a permanent improvement. Honestly I find the onboard experience comparable between the two and LHR offers, for me, more convenient timing as well as better privacy in the seat and the chance of an op-up to F.