We have tile and I wouldn't trade it for plastic in a heartbeat! As another poster mentioned, water hardness is a factor but we have very hard water (lots of mineral deposits) and don't have an issue with the tile being clean at all. Key is to seal the grout extremely well. THAT's what really gets gross. I wish I had followed the store's recommendation on our shower walls re sealing but we didn't get that advice until we were doing kitchen floors! Their recommendation was to use 8 - yes 8 - coats of grout sealer. I did this to the grout on our kitchen floor and it is a breeze to clean - no extra scrubbing at all. Our bathroom grout really needs to be removed and replaced but we're never out of the house long enough for this process to be completed so it's just a cleaning headache on that end.
My experience with the plastic walls over the years was horrible (in various apartments in my former life!). But one recommendation I did get for that - much, much later - was to use car wax about 1x/month on the plastic shower walls and they are far easier to clean. Use a non-abrasive cleaner if that is the route you decide.