When I was at LV store I ended up buying the Speedy 35 Damier. The 30 was too small for me. Also I tried with the bandoulière and those bags are big as a cross body.
Once home I am so glad I got the 35, fits all my stuff.
As for the size, I forgot to mention that I'm 5"7' & like really big bags but the 30 was good for me. However, if I could go back, I'd probably get the 35 for the extra room.