wow that's a though choice, they are both perfect!!
I have the tivoli gm and it is the most perfect monogram bag IMO, but if you are not really into monogram, I'd go for the Chanel. I personally think it is a disadvantage it doesn't have a top zip, but other than that, it's gorgious too!
I have that bag in MM and cream/snake logo. Mine has a zip top - so I can close it up.