I definitely think I'd like both (not having had the opportunity to give my girlfriend an enema). I know the interest started with anal play, and an interest in enemas was an outgrowth of that. Unfortunatley, my girlfriend isn't really that into anal stuff. She indulges me, and sometimes I get to rim her (which I love), and I can usually get away with fingering her ass for a minute while going down on her, but I rarely get the chance to slip more than my fingertip into her. We've never had anal sex (although I'd love to), so I doubt there will ever be a time when I get to give her an enema, either.
Mostly, I'm just enamored of her butthole. I think it's absolutely adorable, and I would love to spend time just focusing on it, worshipping it. One of my deepest fantasies is to see her anus penetrated, with my finger or tongue or a toy. I'd love to see her little hole spread and circle around something, and watch it sink into her. The few times she's let me put my finger up her butt, it was incredible--she felt so hot and tight, and when she came I could really feel her squeezing me.
The fantasies sort of evolved into activites that would be all about focusing on her ass, and I could really take my time and look at her and play with her--medical stuff like taking her temperature rectally, or giving her an anal exam. Giving her an enema just seemed a natural extension of that. I don't have any scat fetishes, so it isn't about that (I don't know if it's about that for anyone else here either, or if that's even usual for people into enema play). I just want to take my time with her and do something really, really intimate.