I'd say both if you have the time. Try to know everything in the packet- it really has the main info that might show up. Some of the practice exam questions you might never expect ended up being on the real thing (possibly in a different form, but the subject matter/answer the same), so I was glad I did them all. Aside from Dr. Collins material, maybe study a little more about the nitrogen cycle, fungi, and maybe some anatomy (specifically what different organs do).