The Rubi v Sigma debate will never end. I happen to be Rubi supporter. Not really against aother makes, to me it's a question of what is the best working tool for an individual, I simply slow down using single bar cutters -at my age anything that tends to slow you down is a clear disadvantage.
Over the years I have met a fair few tilers who have many more years experience than me - the split between camps was pretty even. But whichever camp they were in - Sigma or Rubi, they were totally against the opposition.
But I have the definitive advice for anyone thinking of buying a new manual cutter -try both. The best cutter is the one you are most comfortable using, cuts accurately, reliably, and quickest when you use it. It's never a good idea to simply follow the advice of others, what works well for one may not work well for another.