I have a 14.2 cob which i share with 12 year old ds and I wouldn't swap him for the world!
I'm 5'4 and usually 9 3/4 stone... 14 weeks pregnant now so more like 10+, but still fine to ride him. Ds is 5'3.5 and 6 stone!
Coblet lives out 24/7 (may well come in in the really grotty weather dec-feb), only gets haylage when he is in. Touch wood, has never seen the vet apart from routine things.
He is small enough for ds (we have had him 2.5 years). He is small enough i can hope on and off when out hacking, when i inevitably drop my stick, need to unpadlock gates... or fall off whilst hunting!
He has done PC, SJ, XC, and DR, at local but respectable level- he was placed in C+T finals 2014.
He is the sweetest boy ever and a doddle to handle. Ds does everything with him handling wise and always has done- bring him in/out, load and unload him, all grooming/tacking up by himself.
The downsides are that he is a ridiculous colour- far too much white for such a mud monster!! He gets super hairy so needs a lot of clipping, and he eats ANYTHING so we have to be strict about treats or he'd be nose deep in pockets constantly.
I think but it may just be the limited no of horses i have met, that a good cob is less cheeky and less likely to try it on test you than a pony... but they do have a bit of a stubborn streak!