Hm, I was contemplating whether or not this was relevant to A&D, but honestly, it sounds to me like you're looking for inspiration and opinion on what direction you should go with a piece (granted, a different medium). As long as you're not trying to sell your shirts here, I think there's a lot of potential for discussion in this.
Personally, I would want a shirt that represents the things I like about Pokemon as a 22 year old girl, but that may not be in demand. The kind of Pokemon you choose should depend on your customer basis.. but I think there's a lot of room for grungy Pokemon art out there. I would want something that captures the competitive edge of certain Pokemon, and showcases their skills beyond what the anime displays.
I hope all of that makes sense! If you can tell us a list of Pokemon you're considering, maybe we can help you come up with good backgrounds and appropriate text for them? Keeping in mind what would look good for a t-shirt as opposed to paper makes for very interesting conclusions, in my opinion.
