As nobody else seems to care I'll try to help you out. The problem is that I know neither Act VII nor Believe and basically don't like Crematory very much. But I DO know all of their albums from 1993 to 1997, so I'll try to fill you in on what I think about these albums -
Transmigration: Their debut which is pretty much just another decent Death Metal-album with keyboards. Not like Nocturnus, of course. Crematory have always kept it nice and simple, as you probably know. It's one of their better efforts in my humble opinion.
...Just Dreaming: The second output which I think is by far their best. The songs differ more from each other and the sound is better. There's also a song with German lyrics on it. Overall it's still Death Metal with a heavy edge but the keyboards have already started to take over and push the guitars into the background.
Illusions: The third album is their most requested one over here in Germany. I could never figure out why, 'cause to me Crematory's quality started to decline with this one. But that's just my opinion. There's a song called Tears Of Time on this one which seems to be their biggest hit. Again the keyboards became more important so lots of the power was lost. Back in 95 this stuff was called Death Metal-Pop. A pretty good description, I think.
Crematory: This is pure crap. To me all the tracks sound like kids' singalongs with growls. Nevertheless there are many who appreciate it a lot. The whole album is in German and was said to be a gift for the German fans' loyalty. In terms of style it's pretty close to its predecessor.
Awake: A step back from their last two efforts and a bit heavier than before. It's well produced and again much praised by real fans, but somehow it never really grew on me. It's better than it's predecessor though.
If you ask me for advice then pick up their first two albums which sounded a lot darker and not so much like happy children's tunes. Hope I could help you at least a little bit. Cheerz!