1st choice would be whichever has upgrade space.

I just came back in CW LAS-LGW was the cw with no usb ports and that very weird plug socket which only seems to take an american plug. Arriving at LGW with 6% battery and trying to order uber was fun!

Given the chance of being in wtp the whole flight I'd take the LGW flight, because it leaves earlier so you're not naturally trying to sleep. Over night in the wtp from vegas is my idea of hell.

Finally, I find the new WTP seems to have horrific lumbar support, and every time I've flown new im in agony when I land, whereas old I dont seem to get that as bad. Whichever route you take make sure you take an ipad full of your own stuff. -I was moved from my cw seat to a new one due to faulty ife before take off, and the last time I flew to LHR they had to put the movies on loop.