Definitely Invisible.
I seem to be in the minority that thinks it's the best NG album. I really dig the Deep Purple/Uriah Heep influenced style on it, and it has a ton of songs that I love (To the End, Misery, Still Alive, Raincheck, Stalingrad).
WD is a great album, I haven't really got any complaints about it, it just has fewer tracks that really grab me. The title-track is a masterpiece though; one of the best songs I've heard this year. I love the packaging too - unlike most hard rock/metal albums, it's very simple, classy and tasteful.