I would like a rival to be a female in all cases. I'd really like her to be mysterious, kind of like silver just not power crazy. When you first meet her, she'll be doing something you conceive as "bad" or "evil" such as breaking into a pokemart or something, and you stop her. Then, she respects the way you love your pokemon and self proclaims herself your rival. As the story progresses, she'll challenge you more and you'll see her doing more bad things. By the climax, all the bad things she did willl be revealed to be for a greater cauuse, to save the legendary or something, and you find out she's actually a really good person.
Interesting.
Frankly, I'd want to have 2 rivals. Both rivals that actually challenge you. I don't like the way they potray the rivals in previous games. Gary was going "Smell ya' later! but here's a fame checker." Silver is like "I'm clearly better but why are you always winning? D:". Don't even get me started on Lyra. I don't want a pseudo-rival who calls and say that her Marill has evolved but clearly not. May and Wally, which one's your rival again? I like the concept but the way they portray it is like, wtf. Wally wants to get stronger so he disappears with Ralts and stops you at the Victory Road. May is good, as she can be battled optionally, too. Barry is nice, but he alwats scares the hell outta me as he randomly bumps me. Dawn's Pokemon are weak but you double battle with her?
Maybe, I'd want something like this:
Rival A is the opposite gendered character you didn't choose and Rival B is the main rival. Rival B would appear from nowhere and challenge you from time to time, while Rival A would appear at random times with nothing major going on and can be battled optionally and would block you from entering a building if you goes ahead of the storyline by battling you. (Think of May in the Lilycove Dept. Store) and maybe some characters would imply to you about a love interest of Rival A for you (Dawn, comment from Mars and Lyra, comment from the day care elderly.) You, Rival A and B try to become the champion with you as 1st place, B at second and A for third. After that, you can battle B at Sat and Sun while A at Tues and Wed. Before entering the battle frontier, a double battle will commence and you can pick a partner, whether A or B. And you can team upwith them on the Battle Tower, too.
Asfor their attitude, maybe like Barry. You friend but mostly your rival and May, helpful but can be an obstacle. I hope they don't make it like Leaf, where she disapppears throughout the game.
Although, I'm just fine if they make the pseudo-rival having decent and gender neutral Pokemon. (Am I the only one disturbed that Lucas uses Clefairy as a main Pokemon and Ethan running around with a Marill?)