Knit flat and sew? Knit in the round seamless? Knit flat on straights or circs? Knit in the round on dpns or 1 circ or 2 circ? Knit both at once, flat on the needles? Knit both at once on circs? Knit both with steeks between them, cut the steeks and sew the seam?
Seems so simple doesn't it? Two tubes, wider at the top, sewn or otherwise attached to the sweater body, and that's basically it for sleeves.
When I make baby sweaters, I make them seamless preferably top-down since there's usually not a shoulder seam that way, although I've done them bottom-up and sewn up the shoulder. Baby sweater sleeves are almost always seamless. Elizabeth Zimmermann's Baby Surprise Sweater and Surplice Sweater have shoulder seams, but sewn carefully, there's no seam bulk so ok. I did do one top-down baby sweater with flat sleeves with a crocheted slip-stitch seam, easy enough to do, but more bulk than I like for a baby sweater. So, baby sweaters that I make, with few exceptions, are seamless, with sleeves knit in the round on dpns. But then, a baby-sized sweater body is smaller than an adult hat, and sleeves are maybe 30 stitches. Easy to maneuver on dpns.
Adult sweaters, on the other hand, I haven't made many of. Only finished one actually. Well, two, but it was the same sweater - I didn't like how it looked finished, so I ripped it ALL out and re-knit. And it wasn't even for me! That sweater I did completely seamless. The body on circs and the sleeves on dpns. Hated it. Doing the sleeves in the round meant corkscrewed sleeves/sweater and untwisting them every few rows. Turning it clockwise then counterclockwise would've helped, I'm sure, but since I was knitting clockwise turning it counterclockwise after each dpn went 'against the flow' so to speak. Same with the body.
And I don't care what people say, when using circs the weight of the sweater WAS noticeable, it's not laying quietly in your lap. It's pulling on the circs, it's getting twisted from turning the circs as you go around and around. The circ cable twists and kinks even with the sweater weight, and undoing the sweater corkscrew and cable kinks is not pleasurable knitting, even in plain stockinette. (why, no, I don't much like circs, could you tell?)
So, I just finished one sleeve on the Thora sweater I'm making. I did the sleeve flat, on straights (14" Lion Brand) at first, then switched to Clover Jumper Flex needles. At the end of one row I turned clockwise, the next row counterclockwise, so no corkscrewing. The 8-row cable only had 4 rows to keep track off since the 4 wrong side rows were all "knit the knits, purl the purls" it didn't matter if I was on row 3 or row 7, all the ws rows are the same. I just need to track 4 right side rows. Done flat, that's easy. Done in the round, that's 8 rows, in a pattern that for me, is hard to read and tell which 'non-pattern,' aka the wrong side row, I just finished - so row 3 or row 7 DOES matter. Knitting flat simplified the cable for me. I'm sold, adult sweater sleeves, knit flat on jumper needles. At least for sleeves with a cable, maybe I'd feel differently about sleeves with a different pattern. Sewing up a seam is a small, very small, price to pay.
Haven't decided on the body yet. I'm knitting the sweater top down following Barbara Walker's directions for a peasant sleeve with a square armhole.