What size CS & PP do you usually buy? If it's 12x12 then I'd go with the Cameo because it gets to be a PITA to have to cut down the paper. I had to do this all the time with the Silhouette SD before I got my Cameo and it drove me nuts!
Have you ever thought the SD card slot is a good feature to have? If so then go with the Cameo because the Portrait does not have one and HAS to be connected to a computer to cut. I don't use the SD card often, mostly at crops, but it's certainly handy because I don't always have room for my laptop next to my Cameo at a crop.
But I honestly can't recommend the Portrait because it's just so nice to have the extra 4 inches of cutting space (not because there's anything wrong with the machine itself, I just love the extra space). I realize you only plan to cut titles, but you just never know--you may love the cutting ability of the Portrait so much that you want to cut more and more things, but you will eventually get stuck because of the size. There were so many times with my SD that I got so frustrated because I couldn't cut bigger than 8" in both directions. Sure, I could cut 8x10 or 8x12, but I love being able to cut 12x12 because I love the look of a background cut with the same CS as my base CS...a very neat effect.