Im looking at both these brands too, Im not so much trying to make a choice in the same way though, my thoughts are:
Sugarpill has a smaller line, this is not a bad thing, it means I can justify buying between 5 and10 of my favorite products which will be high impact pigments or a few of the distinct eyeshadows.
I will buy Inglot more as basics for kit, these are I believe cheaper than MAC and of comparable quality. They have magnetic compacts which can all stick together so ideal for kit.
In terms of purchase, Sugarpill is only available online but with so many reviews and tutorials online you wont likely get something that looks different from what you expect.
Inglot is hard to buy in some ways as such, with less reviews and so many more products, limited shops etc and no website in the UK. Unless you live near a store or can justofy the trip, or you live in the US I think they do run a US website, I dont think they ship internationally though. So if you can get to a store Inglot its a good choice at reasonable expense. I dont think they do pigments though which is the highlight of the Sugarpill range.
So as I said I will buy some Sugarpill AND some Inglot but they will be different products. Maybe you dont have to choose between them either ;-)