It'll be the Jedi Knight. One of the last JK companions is a big tie to the Revan novel, as is the final JK boss fight. Won't spoil either, but those facts alone make it a major tie. Plus Drew K. wrote most of the JK story himself, so it has the commonality of the writer.
Every class gets some interaction with the KotOR stuff via the mid-30s flashpoint chains(Taral V/Maelstrom Prison for Reps, Boarding Party/The Foundry for Imps) though. But JK ties strongest.
"Sir,we are beginning our search for these rumored 'underwater villages'.They will not stay hidden for long". -Battle Droid Commander OOM-9!