I have come across Sankyu variations from the various Aikido styles.
This is not a question of styles but of situations, possibilities or also preferences of tori.
And there are lots and lots of ways.
Basic way I (being aikikai) try to practice is palm faced out on my shoulder (or maybe even higher because I'm not very tall), fixed with one hand, other arm as much vertical as possible, pointing downward. Nearly no twisting or spinning.(Whats the difference in this case?)
You can do sankyo also standing with your knee or "half kneeling" with your thigh.