Robert in Stage 5 and 6 gets extremely cheap, and I mean cheap. No expert out there and do what the Robert does. All I can do against him is go aggressive. Once he gets the best of you and puts you on the defense, you're history.
Oh, if you try to roll past him 60% of the time he'll try to grab you, so throw escape and then send in a striker to juggle off the throw escape (note this does NOT cost a DM stock, only a striker stock) and do whatever you want.
Choi - The stragety I use for him worked in '99. If you're near him, try running at him. Sometimes this will cause him to jump (just like how a bug runs away when you try to stomp on it). If you use a character with a fast C (Kyo, Clark) then you'll get him when he tries to jump. Or else just turtle and use your character's best anti-air move when he tries to jump in.
Vanessa - Oh boy. The AI really makes me dislike boxers. My Iori is most effective against her. She teleports around a lot, dodging a lotta my attacks. However, Iori's QCF + P fireball thing hits her out of a lotta her moves since it travels along the ground (which she's not invulnerable to). Otherwise use grabbers, she may be invulnerable to your moves while teleporting but a grab always works!
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I eat King sized pancakes for breakfast, Terry-aki burgers for lunch, and meat Jhun with sloppy Joe and Kim chee for dinner. All I need is Kyo to BURN'em.