I guess one of the things that makes Lorenx's question complicated is how you'd define the different manga categories in the first place.
According to TVTropes, the different categories of manga you mentioned describe the age and gender demographics rather for manga rather than any particular type of genre.
If we
were talking about genre, then I agree with Litt. There's enough merit to just about every genre I can think of that I'd love to dabble in every category that I can muster. Part of that would be to work within the genres that I like, but also to challenge myself to
become interested and create something that's uniquely my own in a category that might not have had a perspective like mine otherwise. In that sense, my answer is "no." There's no category of manga that I'd want to avoid.
HOWEVER, if we're talking about categories of manga in regard to demographics, then that's another story altogether. In this case, my answer changes to "Yes." The Shoujo category includes girls from about the ages from 8 to 18, and trying to write a story that's specifically and intentionally designed for that group scares the poop out of me. Now, again, I'm not saying that I wouldn't avoid it alltogether. There's a great story opportunity here somewhere, but I'm just not as eager to jump into writing a Shoujo story. I'm afraid that what I ended up creating would be more of a Mel Brooks-like parody/homage to Shoujo than an honest-to-goodness Shoujo story. To make a more Western-centric comparison, it'd be like trying to write my own version of "Twilight" without making fun of "Twilight" or it's fanbase.