I just bought my first agenda yesterday (azur) and returned it today for an Epi. I got the small size, it's large enough for me to write in, yet small enough to fit in my bags. I have a palm pilot so I don't expect to write EVERYTHING in my agenda but we'll see. They come without a calandar. The calandar inserts are about $60 extra. A lot of people here will tell you to order from filofax.com, as I did yesterday, and today I checked my local Staples and they had inserts that fit. Filofax had a nicer selection though, so I recommend it!
I chose the epi bc it's durable. The azur would have been too lite in color. I hope that helps somewhat!