Here is something I wrote a while back for a friend who was debating between the two bags.
Speedy 25:
Pros: very roomy and is great for casual wear, very grab and go type bag, yummy red textile lining!
Cons: will sag unless you put something on the bottom (unless you don't mind. I actually like it.), handheld means you always have to hold it (can be a pain when shopping), heavy if stuffed full. Opening might be a bit narrow for some people to keep sticking their hands in and out.
Also, kind of random but if you have very sweaty hands, the leather handles on the underside will wrinkle more from all that holding and sweating and rubbing! Eeeew. LOL.
Papillon 26:
Pros: sooooo cute and feminine, good for casual and more dressed up occasions, cross-grain leather interior so I didn't have to worry as much about getting it dirty.
Cons: not as roomy as the speedy but I can fit my phone, a small cardigan, wallet, keys, a bottle of water. It was pretty packed though like that. Can't put any books in it and probably not an agenda unless you have a mini. Also, the shape is not conducive to organization of any sort so your stuff will just roll around and if it's stuffed full, you will have to dig through your bag unless you keep them in pouches. Also, it's only a handheld bag.
I have them both and I love them both! If you want a functional, everyday bag, go for the speedy. If you just want a cute bag and you don't have that much stuff, get the papillon!