I use Sigma Down here can't remember how many I got maybe 10 or so I usually keep a 35 and a 75 in the truck they cater for most jobs.
They both have there pros and cons
rubi pros
Novice tilers would be better sticking to a rubi as they require less skill in snapping pressure wich is a big plus for rubi. They also have good visability to line up cutting marks due to the dual bars. Also there slim design make them compact and lighter to carry and work well in tight bathrooms.
cons
Prone to flex on thicker tiling material, also more moving parts, they need regular maintenence. The double action can be a bit annoying at times
sigma pros
Built like a mack truck, little maintenance required, less moving parts, will last a lifetime, The perfect single action, good handle and wheel design, will not flex, quality sprung tables. quality compass
cons
Can be hard to use if your a novice, heavy and wide, you have to tilt the head to line up cutting marks due to single bar.