Which version is more reliable?

I've got different simulation results of a specific simulink model with different matlab versions. The result of 09 version is better than 08's. Which result is more reliable than the other one?

P.S. Searched on the website, many similar problems occured. Hope to get a certain answer.

[Kaustubha Govind]

It's hard to tell without knowing which blocks are causing the difference, and exactly how different the results are.