Personally I'd go for a discounted SP5 over a Surface Go, unless the usage was very light. I looked at both SP6 and Surface Go; one too much, one too little performance. By chance I came across an Acer Switch 5 (i3, 4Gb, 128SSD, with backlit KB & Pen) more powerful than the Go and far cheaper.
I just need something reasonably small & light with Touch & Pen to toss in the bag while I'm on the rounds with the contractors, nor something I want to be overly concerned about. So far the Switch 5 has met my expectations for a lightweight system which is all it really needs to do
I added a 256 MicroSD which takes care of any media storage.
Although the Go has more RAM and faster SSD the CPU can really bottleneck the system. As ever much is dependant on the usage. I like the Switch 5's port solution as although a W10 tablet (2in1) it has USB A, USB, C, power & MicroSD. The 2.7GHz i3-7130U holds up well thx to a good passive cooling solution, hyperthreading (4 threads) and HD 620 Graphics. So far the 4Gb has not been an issue, equally 8Gb would be preferable, however at just $650 US there is absolutely zero to complain about with the Switch 5.
If I was looking at a solitary 2in1 I'd opt for the SP6, as it pretty much ticks all the boxes for a 2in1 detachable device. I did consider, but it seemed overkill for the planned usage and my primary field notebook a very performant 8th Gen hex core coupled GTX 1070 and 32Gb RAM, and the Switch 5 can double as an extended display for it's more powerful sibling
Switch 5 has i5, i7 options with greater storage, however the benefit of the more performant CPU's is marred by throttling unless one's workflow is "burst" focused. Pricing reflects the hardware bring the Switch 5 closer to the SP6 although KB & Pen is included. Display is best if calibrated and certainly benefits. Without a doubt the Surface displays are superior, equally once calibrated the Switch 5's display is a very decent 1440p experience with HDR. Those needing more storage the Switch 5 is upgradable with a little care and patience thx to utilising a standard M.2 SSD & removeable rear panel
I did briefly consider the new Air, however Apple's poor spec, underwhelming usability, unreliable keyboard and rather humorous pricing made it very brief interlude indeed
Q-6