Comfort wise I would say the Monty, style wise the Tivoli is really nice. I bought the Tivoli GM and returned it for the Galliera. It was not working for me and when I tried it at home the straps on the Tivoli kept slipping off. It's a really heavy bag as well. HTH
I only know about the Tivoli GM b/c I have that one. It's lightweight until you put a bunch of stuff in it. Then it does feels heavy & I have always kept my straps to the longest setting so it doesn't slip off my shoulders as much as others mention. That helped me anyway. It's details are so pretty too. (sigh......) good luck deciding!
I've had both and love both.. I've sold my monty gm but want to re-purchase it because I miss it! I think the monty is like a speedy with shoulder straps, it holds a ton and if very comfy to carry. The tivoli is easy to carry, holds a ton, and stylish... I think the tivoli is more like a "ladies" handbag IMHO. The prices are significantly different. I think the tivoli is now around $1600, and the monty gm is not nearly as much. Let us know which one you end up getting! =))