I agree with Republic Corellia. I loathe the planet itself - obstructive design, claustophobic, orange and brown and brown and orange, and generally a deeply unpleasant place to finish one's journey through the story (ok the park has its moments, but not enough). But I still have really fond memories of running through there with my main, because it really did feel like such a triumphant capstone to the war and the epic culmination of everything I'd been working toward. (Plays really nicely with the JK questline, too, which always helps; I tend to enjoy planets less when the class story and planet story are completely disconnected or thematically at odds.)
I also really like Ilum, if only because the idea that the story doesn't stop at 50 and there's a whole well-developed plot with characters and progression and stuff to do beyond the level cap and not just repetitive raiding or PvP is so great.
Illum was alright,Malgus was pretty cool though