Currently, I'm just looking to write. If it's something outside my normal writing styles / genres (which I will admit I can't exactly label although historical and modern fiction major heavily alongside sci-fi and "adventure" style stories) I will do my best to complete the task.
For example, I am more used to writing adventure or philosophical stories. However, if you wished for a horror story, I will do my best and see it as a challenge to increase my repretoire, so to speak.
I guess the moral of the above is that I have no set limitations or rulings as of yet. As for what would challenge me more... I would have to offer the non-answer of "I don't know." I enjoy all themes of writing as it's more the story that entrances me, not the mode. It's the interaction, not the setting.
Feel free to ask for pretty much anything.
UPDATED:
Currently, due to a surprising number of requests within the past few hours, I have several stories to write. Here is my laundry list so that I can point to it and have something for everyone to see. It's listed by either Requests or Trades and how that request was received.
Requests:
ThisIsGabe (FA - Note)
Rigor (FA)
Puncia (PM)
Trades:
Ventus Fall (PM)
Reno (Text)