In general, shinobi feast provides a 'steady gain' in terms of coupons. It has a few slots filled with coupons, usually 1-2 with frag(s) of itachi and lately, whole ninja as jackpot prize. It used to have fixed rate for 100 coupons at first draw, so it was a really efficient way for low cashers to gain more (300 additional coupons while recharging 3 days in a row for monthly card is one of the best recharges for low spenders). Heavy cashers could capitalize on getting multiple coupon prizes and some of SR frags (shinobi feast is the most efficient way to get susano itachi till date). Slot machine on the other hand is pure rng, that offers items instead of coupons (while average refine rune or lv4 mangatama can be useful, you wouldnt buy them if you were given equivalent prize of coupons). It offers jackpot prize as well as shinobi feast, as well as 2nd place 30*susano frags which can speed up the process of getting sasuke by a lot. 3rd prize obviously is the most common of jackpots, however it offers a gain in 200-500cp range.

Personally, I'd chose shinobi feast over slot machine every single time. Even though both are rng events, while rng jackpots quality tend to favour slot machine (unless the goal of recharge are itachi frags), we all know how rng in this game works. I'd pick shinobi feast, because it gives currency which you can spend however you see fit, instead of unoptimal prizes like mangatamas or moods.

Can't remember, haven't seen this event in a while now.