I know what the full scale books say about Hoerner wing tips and end lates, but they don't know beans about Sport RC flying. I have flown both Hoerners and plates for over 30 years and for sport flying, you want plates. They work in both directions, upright and inverted.

I have tried fancy carved Hoerner's and just downward end plates and couldn't tell and difference. I will tell you this. Hoerners and downward plates will decrease your dihedral or add in an anhedral component. I use them on high wing planes like Sticks to compensate for the high wing location, stopping roll due to rudder.

As for block tips vs. flat tips, I ran some home made wind tunnel test many years ago. A friend of mine made a tunnel and glued threads on the leading edge of the wing. His wing had plug in tips so we could try different types. We didn't have and lift or force measurements, but we could see the path of the threads. These gave an indication of the outward flow and the tip vortex.

The big rounded, 1920's-1930's type tips were the worst, having the most outward flow and threads curling around the tips.
Stick type tips were next worst. Fairly good amount of outward flow.
Block wing tips were next. Some flow.
Flat ends were next to the best. Very little outward flow.
End plates or Hoerners were the best. No outward flow.

End plates also increase the roll rate, slow the landing speed and make it harder to snap and spin.

This wasn't very scientific, but is was enough for me to quit wasting my time carving any more tips. Pretty was not the best.