Could anyone advise?

I've been working in Maya 4.5 for the last couple of years and am more than aware that the renderer is not as good as other 3D software packages. Working on a joint project with some Lightwave artists recently highlighted that.

I was thinking of upgrading to Maya 6 so that I could use Mental Ray.

Could those with the experience tell me the pro's and cons of Mental Ray and is it worth the price of the upgrade? Does it compare wellk with other renderers? Or do I import all my models and texture maps into Lightwave to be rendered?

Thanks
R.