This question is similar (it was Surface Laptop not Surface Book) but you may still find the discussion useful for your decision making.
I answered there in more detail but to summarise:
People can quibble either way on some, but generally in 2018 these rules still apply:
WWDC has come and gone without any new hardware and to my knowledge there are no reliable rumours of Surface updates either (aside from a budget model). I suspect both will get updated around September/October but they may come sooner.
The MacBook has well documented keyboard issues and the Surface Book is bizarrely missing Thunderbolt and has some quality issues of its own (like an unreliable power button). It is a frustrating game of waiting as the next round of updates will very likely address these issues and be “the time to buy” for MacBook and Surface Book.
If you need to buy now then I would pick either the Thinkpad X1 Carbon or Thinkpad T480s. The reason I would pick the Thinkpad models over the Dell XPS 13 is because they both have slightly larger screens (14"), more comfortable spill-proof keyboards, higher build standards and include a webcam in the right position.
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