I went with 3 strong fighters and Sara as crystal carrier because of her high speed. You won't find new heroes and research is limited, so stock up on food and try to create choke points with your heroes. Make good use of Neurostun and Tear Gas modules.
*** Spoiler - click to reveal ***Just don't pick Sara + Gork since one of them dies after several levels (whoever is first in the lineup). The same applies to Josh + Max + Troe + Warden, as either Warden or Josh dies (again whoever is first in the lineup)!