Timothy Zahn definetly wrote the best ones out of all of them, Thrawn was such a complex bad guy. Supposedly there are a few Thrawn books that I have never been able to find though.
I loved these ones. Thrawn was so cool, and those little ninja death claw creatures (i forgot their name, but they were SICK!), and the ysalimari...whew! that was good reading!
Oh, I forgot to mention Joruus C'Boath!