I think Leprosy is their best pure DM record. Symbolic and Spiritual Healing are transitional albums and they kind of suffer a little incoherence because of it. Individual Thought Patterns is my favorite Death album, they kinda set the template for progressive Death Metal with that one.
The Sound of Perseverance really isn't a pure Death Metal album in my eyes. A lot of NWOBHM and straight Rock and Roll influences in that one. Listening to it, you get the feeling that if Chuck hadn't have passed away that Deaths days may have been numbered as a band. It sounds like Schuldiner may have gotten to the point where there was really no other direction that Death could have gone that didn't compromise what the bands original intent was.
I think if he would have lived to continue making music, he would have abandoned Death Metal completely and moved on to something else.
Which would have probably been great too, because he was one of the most original and creative musicians metal has ever seen, and I'm very sad he's dead.