Home Forums Mac Software Mac Operating Systems SL to ML?

I am quite happy with OS 10.6 except for one problem. avi movie downloads have to be converted because of the appearance of 3ivx Trial (in red) on the video. I convert them to MP4s and they are normal. Even the movies I downloaded before SL became defaced by these red letters. I am wondering if upgrading to mountain lion will resolve this issue. Apart from that, Is ML better than SL?
What advantages is there and does it warrant the difference?
jaybass