[2001MUgrad]

I'd have to agree with Carl Lindner, but
I assume you are talking about other teams.. So.. Its really hard to have a rivalry when you suck. Just ask the Redskins, it used to be down and dirty with Dallas 2 times a year, but its hard to be a rival when you never win..
With that being said a few years ago the Astros where pretty close, a few heated series between the 2 teams and a couple of bean ball games.. but then Reds started to suck and suck bad..

So, I'd have to go with Cleveland as far as most Reds fans are concerned, but with the team itself I'd have to go with getting up in the morning as their biggest rival, it must suck to see your name in the paper with blown save beside it or an L, or 2 or 3 E's or 3 or 4 K's.