Sammael is one of the 2 half-decent named characters in the codex.
The jetbike rarely does much other than draw fire. You might get lucky with the plasma cannon, and even if you don't, its presence in your army, while a bit random, does at least force your opponent to un-cluster deep-strikers rather than attempting to shoot... but that's not worth 205 pts. His
CC abilities are nothing to write home about -- he's OK, but again, not worth 205.
The speeder gives you consistent, powerful anti-infantry fire for most or all of the game, unless you're very careless or unlucky. You should hit with 6-7 shots per turn. Unlike a pred, you can shoot on the move. If you like or need to, you can threaten side armour with him pretty easily too. It's still not worth 205 pts by itself, but...
...what you really take Sammael for is unlocking bikes as troops. He's the only way to do that with the
DA codex. So if you want a bike army, he has to go in there. Personally I'd use the speeder version if I had other armour in the army, or the jetbike version if not.