for me, it depends on what i'm going to use it for, that day. i have two 25s (mono and cerises) and a 30 (white MC). i barely use the 30, only because it's MC and i kinda lost interest in it. i do still use it when i want to carry more things than usual, like an umbrella and a water bottle for my puppy, but usually i use one of my 25s and those extra items fit in fine (and i carry a lot in there!). i wouldn't, however, mind getting a mono 35 just to have...