End plates are great. Their disadvantage is that they add a lot of wetted area. The cutoff tip or Hoerner tip add no or little wetted area, respectively.

End plates generally add more drag than they save lift. An engineered tip can be looked at as adding to the effective span of the wing. End plates add about half the lift that would be added by simply extending the wing out their height.

Winglets are designed for a single flight condition... away from that and they lose efficiency fast. The nice thing is that winglets can actually save double the lift that would be had by simply extending the wing out their height.... but again... that's for a single flight condition.

Weight is another factor. Hoerner tips and simple cutoff tips are lighter than your typical plastic end plate.

But again... simple question... simple answer... cutoff tips (or better, Hoerner tips) have less induced drag than rounded ones.