To me, a sports rival is a team that you hate with every fiber of your being.  In college, it's Dirt Burglar Community College (a/k/a OU).  In baseball, it's the Cards.

The NFL is a bit different for me, because I have so much hate for so many different people and organizations.  I will always despise Bud Adams, but I find it impossible to hate the Titans anymore because of VY's presence there.  

I definitely don't like the Jags, and they're probably our truest rival in the sense of a divisional opponent that brings out the best in you.  

When it comes to a true, gut-wrenching, rage-inducing opponent, however, there's nobody like Dallas.  I abhor everything about them, from their owner to their fans (not the true fans that stuck with the team through 1-15 in 1989, mind you; it's the bandwagon frontrunners that I can't handle).  So Dallas gets my vote, though you're totally right in that it's a one-way street.  The Texans haven't done enough to warrant any sort of heat with anyone, save maybe Jacksonville.

I hate the Cowboys like I hate catheters.  But I'll hate the Titans with a passion until that selfish old mo*#$#!#* @#($#^@$@ ^@##$(@sucker Bud Adams dies.  As I have aged, I've become a pacifist.  I wish nothing but the worst for that POS.

That said, I voted for the Cowboys.  I'll always hate them.