Personally if by Rocklers you mean the CNC shark, I wouldn't even consider it as anything approaching a cost effective or economical option. IMHO it's a way overpriced machine, especially for the materials used in it's construction. A Chinese 6040 with the rubbish supplied controller upgraded to a Gecko G540 is a far more cost effective solution, at less than half to a third the cost, and built with "real" drivescrews and solid aluminium construction.
The Probotix and Romaxx (the romaxx does look very nicely constructed) I can't comment on personally as I've never seen one in the wild, but I have heard good things about them. But then again, some people seem to love the CNC Shark, so I guess it's all relative.
Forgot to mention, so far as software goes, if your serious about potentially building a business doing signs and engraving, or even just having fun, you cannot beat Vectrics products, V-Carve or Cut2D for simple work would be ideal for you. The money it costs is really well worth it, because of the relative ease with which you can create just amazing work.
cheers, Ian
It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!