In reply to MrToffee:
I'm going to be annoying here and ask what you mean by 'lightweight'? You can get a shell that weighs around 100g; anything under 200g has to be considered ultralight by most people's standards; and I'd say something in the region of 300g classes as bog standard 'lightweight'.
I'll be even more annoying and assert that there's no such thing as 'best'. Whether or not you get on with a particular jacket depends on a lot of factors:
Does it have all the features that match what you intend to do with it? eg. Sufficient pocket space, a helmet-compatible hood, a cut suited to climbing, pit zips... generally the more 'lightweight' you go, the fewer features you can expect.
Is it sufficiently breathable for the activity and conditions? It's easy to make a jacket that's comfy when strolling along the flat in cool weather, but walking uphill in humid conditions, or running, are a sterner test of breathability. If you're working hard enough all shells will get clammy eventually, but some are obviously better than others in that sense.
Does it fit you, personally? We're all different shapes and sizes, while jackets only come in S, M, L etc. Not every model will fit every user equally well. Is there space inside for other layers, if it's cold? Is the hem long enough to properly cover your waist? are your arms free to move, and is there enough 'articulation' in the cut to prevent the hem lifting up when you raise your arms...?
We reviewed a load of lightweight shells in 2017, some of which are probably still available:
https://www.ukhillwalking.com/gear/clothing/waterproofs/lightweight_waterpr...
And here's one from summer 2019 on the North Face Summit L5 Ultralight Storm Jacket: https://www.ukhillwalking.com/gear/clothing/waterproofs/the_north_face_summ...
There's a review of the Patagonia Ascensionist Jacket (300g+) coming out in a few days
Also a review of tha Mammut Masao Light (200g+) in the pipeline, due soon
Post edited at 16:56