Quoted from schudel5:I like the white rubber caps for two reasons. The first is they are easy to remove without tools. Secondly, since it's not holding tight, if a ball hits a plastic from below (above a drop target) it lets the plastic move up and hopefully keeps the plastic from breaking.
And to mix it up I dislike the rubber caps for those same two reasons. I find the black plastic acorns looks good on my SI and are easy enough to install/remove by hand.