I don't think either are necessarily better. They are different and my choice depends on what I'm tying to do.
If I'm pretty constipated and my rectum is packed with hard poo, there is no question it's time to get out a bag, fill it with wam, soapy water and get complete relief promptly. A suppository, under such circumstances, would cause a strong urge to poo but not more. It wouldn't do anything to soften the poo or lubricate the passage. At best, the suppository would make you sit on the toilet and strain a lot.
If, on the other hand, you are not very constipated and have a rectum full of softish poo and want something to make you push it out, a suppository, especially one with Bisacodyl, will do that. A suppository also gives fa more play time than an enema and any accidents are usually far less messy.
The latte is especially true if you're playing diaper games. Give a suppository and you probably have at least 15 minutes to play before there is poo in the diaper, possibly a half hour or more. With a bag of warm, soapy water, you're lucky to get 5 minutes.
MO