If your plan is to read both, go with Outbound Flight first, as Survivor's Quest is essentially its sequel. You can probably read the latter before the former, as the story stands up well enough on its own, but Outbound Flight fills in the details that are only alluded to in Survivor's Quest. Additionally, if you read them in that order, it's interesting to see, in Luke's time, how much information has been lost to history over the decades due to the Clone Wars and the rise/fall of the Empire.

As for the Hand of Thrawn two-parter, I definitely recommend them. In addition to being a great read, they do a good job of tying together events from previous novels and comic books (specifically the Dark Empire comics), mainly to get Luke "back to his roots" and lead him away from being the All-Powerful Uber-Jedi he was often portrayed as in previous novels. (There's a great scene where Mara forces Luke to confront the past 10 years of his life, and makes no bones about where he went wrong and where he was headed if he didn't get his head out of his ass PDQ.)

Oh, and a word to the wise: the two books about Outbound Flight do incorporate PT elements (especially Outbound Flight), but IMHO there's not too much to worry about (YMMV, of course).