Both shafts are good choices, 300M, the limiting factor is the CV joint, the 900 cv is half the size of the 570 CV and you plan on doing any kind of racing I would recommend looking into better alternatives than reusing stock 900 CV's.
If you are just playing then LSR on stock CV may be the way to go as they have a lifetime warranty. Holz may be lifetime too, not sure.
If you replace your own axle by extra circlips and be patient. You may want to replace the boots as well depending on when your car was made and which boot material they used.
If you don't feel like Fn with CV's, CV grease, and boot straps SuperATV Rhino Brand axles are a good alternative. Inexpensive, descent warranty, and its a 1 hour job to replace both.