The question depends on the person carrying the bag... You'd have to know basic things to make an assessment for someone else... Sonya, do you like large bags or smaller ones? Do you carry a lot of stuff. Do you like your things to move freely inside or do you like them jammed full?
I have a Speedy 30... It was a fine size for me when I was younger and didn't carry as many things. Now, the 30 is absolutely too small for me. I wish that there was some way I could turn my excellent conditioned French Company Speedy 30 into an excellent conditioned Speedy 35. For me, a 30 just does not have enough room.
You really need to know which bag will accommodate your needs. Good luck with your decision.