Hi
elleLrich,
The mono is a fantastic choice for your first LV!
I had the same dilemma when purchasing my Azur speedy. I ended up choosing the 30 based on advice from friends & fellow TPF'ers, and I'm glad I listened.
Plus, there's not much of a price difference between the two, which is nice.
Here is a thread you can look through for speedy size referencing:
http://forum.purseblog.com/louis-vuitton-clubhouse/the-speedy-modeling-club-show-us-272654.html
I think the best way for you to decide is to go into the boutique & carry both to see which one:
a) looks best on your person (i.e. some might think the 30 is too big/looks like luggage & others might think the 25 is too small, almost like a lunchbox)
b) suits your needs better
c) holds your everyday items better (i.e. the more you put in your speedy, the more it might sag, which changes the shape/look of it).
d) keep in mind that the mono has vachetta leather which will patina over time/use.
If you don't mind building your own patina, go for the mono. If it's a concern, you might want to consider the damier or mini lin.
Hope this helps! Good luck!