I haven't liked any of the methods I've tried so far. The latest one I have tried uses the contiguous method by SusieM, the instructions are available on Ravelry as a free download, here. The Contiguous method is a way of knitting the shoulder seams and sleeve caps of a garment from the top down.
I used a pattern called Avril in April by Reiko Kuwamura which uses this method to create a square necked sweater. This pattern is also available as a free Ravelry download, here.
It was interesting making the shoulders and then forming the sleeve cap. I liked the idea behind this method but until the sweater was joined under the armholes it was difficult to assess how it would fit.
Once joined, I had a lovely armhole shaping but I wasn't happy with the shoulder shaping - far too sloping and the back neck sat too high.
It doesn't look too bad on the mannequin but wasn't right on me. I'm not pursuing this sweater any further - it was only ever meant to be a test knit.
From here I'm incorporating what I've learnt from the different 'seamless' methods I've tried and I'm developing my own idea. I'm knitting up a pattern by Kim Hargreaves called Salina that I made several years ago but I'm aiming to do it all seamlessly with nice fitted armholes and correctly sloping shoulders. It's a lovely pinky yarn and it's knitting beautifully - so far so good.
This search for perfection is challenging - but someone has to do it! I'll keep you posted.