Which lens for reverse macro?

looking for a good lens to do reverse macro for flowers and insect. I am looking at the 20/2.8 or 24/2.8. Want to have higher reproduction ratio, but some said 20/2.8 is not as good as 24/2.8. any idea? AF or MF?

Will also use the reverse lens with PB-6.

thanks ahead

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Vic Lau at Calgary