I vote for the Alma. If you're looking for classic, structured and not too common, you can't go wrong with the Alma. The only complaint I've heard about this bag is the wraparound double-zip closure. I suppose many people find this annoying (just like with the zippy wallet). I've seen women carrying the Mono Alma with the zipper open.
I'm into larger bags but found the Ribera too structured for its size. It almost felt like a structured speedy 35 to me but then again I'm not a huge fan of structured bags. This bag would be perfect for you if you want a larger structured bag.
The Triana is very nice and definetely uncommon, however, I think it is small. I actually considered it once but was dissappoined at the size once I saw it in person. My SA at that time mentioned she never sold one to anyone under the age of 50 and even had the nerve to say I looked older with it. That was rude.
The Speedy 25 is cute but like you mentioned, it is more common and the sag could be an issue for you. I have a Damier Ebene Speedy 30 and I love it. I like a slight sag so I use a Large Purseket with it, however, I have the obsession sunnies too and I find that the case takes up a lot of space in my speedy 30. I usually carry my LV wallet, small agenda, mini pochette, cosmetics pouch, wapity, sunnies, and two other non-LV pouches. All this fits better without the Purseket but then I don't like the huge sag.
Good luck with your decision!