Well, everybody has their own "preferred" method, but I'm not sure you could say that one is definitively better than another... It depends on what your priorities are. Are you just interested in getting the best possible result, or do you also care about how long it takes?
I've mostly done as you describe - sew the body to the sleeve with a 1cm offset, then fold and top-stitch. There are a number of variations - you can iron, you can glue, or you can hand baste. I think hand basting gives the best result, but it takes the longest, especially if you baste twice (once for the initial fold-over of the cap edge, and then again to baste it to the body). Even so, I still struggle to get a keep a really consistent width to the finished seam...
The technique in the linked video, where you fold over the edge of the sleeve cap and sew it in place, then use the edge as a guide for sewing the body, is also recommended by Mike Maldonado in his course. I've tried it a couple of times, and it does seem better - it's easier to get a consistent offset, and it's much easier to fold the seam over. I've struggled a bit with getting a smooth finish, but that's probably because I've not done it enough to get really good at it yet. I also find that it results in a wider seam than I normally like... And yes, it does result in an extra row of stitching on the inside, but does that matter?
Funnily enough, I've just today received a "single needle sleeve attachment" of the sort used in commercial production, which I'll be experimenting with... It's actually two attachments (plus a couple of presser feet, a needle plate, and a feed dog - although I'm not sure how necessary these other parts are): one attachment is basically two guides stacked one on top of the other, which helps you with the offset between the edge of the sleeve cap and the edge of the body, and the other is a folder attachment which turns the edge under as you do the top-stitching from the outside. The two operations are shown here:
(It's very difficult to see what's happening here, as the magic is all on the underside.)
The pattern also going to make a difference - tighter curves are always more difficult. I do notice that these two videos show a very shallow sleeve cap... It'll be interesting to see how well it works with a more curved cap. Of course, this type of attachment is only an option if you have a machine with the necessary attachment fixing point.
Edited by Dunc, 18 July 2019 - 01:19 AM.