We have 3 Prusa i3s with his aluminum frames and they are awesome. You can also now buy a full kit right from Josef Prusa, and it is quite reasonable. We have 3 dual nozzle printers and never use the dual extruder feature. Back in the day ('09-'10) we had plywood and acrylic printers and they did not last long. I would advise everyone to stay away from Acrylic at all costs.

Our Kossel Minis are awesome, we gain some print height over the Prusa at a small loss in build area (X-Z Axis). Both prints well with the same quality of prints. I do love watching the Delta print though!

We have linear rails on both of our Kossils (I have the cheapo Chinese ones and my son has high quality ones). I would not build one without them!