Factory Five GTM engine choice?

What type of engine do you think would be the best choice for a FF GTM. An ls1/ls6 ls2 ls3 ls7 or ls9. And would the extra money be worth it for using an ls7 or ls9 or should you buy a cheaper ls1. I think the Ls1 would be the best choice since it's pretty much based on all of the engines and you can buy it for dirt cheap. It's also a lot of fun to modify and tweak but what's your opinion.