Personally I'd go the VT, but hey I own one, i would say that. The only real problems I've heard about in ths VTI is the power steering pumps, but hey, I don;t think I've ever seen a power steering pump on a holden NOT leak. Essentially the running gear in the VTI was the same as the VS(V6 and V8), except the 5L was upgraded to 179Kw, but the VSIII ute was built along side the VT untill 2000 when the VU came out. The only thing is that the early VTI t6end to be a bit less economical than the later one's, cause they were a bit too heavy to start off with, and the VS is a much lighter car so it would be a more economical drive.
Hope this helps