The best cross colors are yellow, then orange, then green if you pick 1 color from each set of opposites.
This isn’t just some opinion piece either. This is based on color contrast.
With yellow cross, you get white LL with red-orange-green-blue as the side colors. This makes the LL stickers very distinct from the surrounding colors which can help with recognition.
Next up is orange cross. This gives red LL which again stands out and contrasts against all 4 of the surrounding colors.
Then between green and blue, you get 3 warm colors and white on the side so the inter color contrast isn’t as good. Blue is darker than green and this is better for a LL color to increase the contrast as much as possible.
In summary, black op white OO