These are 3 totally different areas. Which one makes sense for you to take depends on your personal situation, your interests, your aspirations, and so on. How should we -who know nothing about that- make a recommendation?
I'd question why you'd jump into 257, as opposed to going with 255 first. With good knowledge of JSPs and Servlets, plus a bit of knowledge of the tool, you'll find test 255 isn't overly hard, although it is certainly a challenge.
I think having a development tool cert on your resume is impressive, especially if you want to get into the IBM world.
I like the UML cert, but I don't think it blows away interviewers. I'd rather have someone who knows how to code an use the tool properly, as opposed to someone who understands all the nuances of a sequence diagram.
SOA is hot. I looked at that cert, but haven't attempted it. I think SOA probably looks best on a resume right now, as every interviewer that doesn't know anything thinks that SOA is the greatest thing since sliced bread. Not to diminish SOA, but it does get incredibly overhyped.