Some poppers come with split rings but most do not. Do I get the best action by tying my line directly to the popper or via a split ring? I'm fishing for largemouth and stripers.
because most do not come with split rings, i have always just assumed that the manufacturer intended them to be tied directly. why else would all crankbaits come with split rings but most poppers do not?

A split ring will give to some extra wiggles for your lure.

A split ring or Duo-Lock snap adds a little extra action to those Pop-R's that can make a big difference. One thing I have noticed that a split ring tends to catch less on grass or floating debris in water than the cross lock snap. While I also use the Rapala knot while fishing for smaller sized bass, I feel that the knot weakens the line somewhat because of the overhand knot required in tying it. It seems to cut into monofilament which is what I normally use while topwater fishing. A Striper or Big Bass will find any weakness in the connection between itself and you and will surely exploit it to get away.