There are loads of threads on these. About a month ago, there was a large thread on montolit vs rubi. I'm a Montolit man myself. I've never really liked Rubi. I chose Sigma over Rubi, and then Montolit over Sigma. Do a search on my username and the word "montolit" and I'm sure you'll get loads of hits
I've personally had a finger in one or two Rubi to Montolit conversions on these forums