Knowing the triplets are all basically the same car, what i have noticed over the years is that Toyota Aygo year on year were a bit more premium in terms spec than the Peugeot 107 or Citroen C1, but they catering for different parts of the market and iirc the Aygo went zero emissions first, had EBD? standard and nicer interior leather bits and better stereo speakers setup, etc. etc. This was reflected in the initial sale price and is usually reflected in 2nd hand prices, but agree with others those Aygo prices are a bit steep, but then depends on demand and where you are, we paid a premium for our 108 cos where we live and I wanted security of a main dealer warranty, but I understood that so had to pay up, but we did have some issues which fair play to the Peugeot dealer sorted without any hassle, so it was worth it and it restored my faith a bit in main dealers after past bad experiences!
Another thing to be aware of, think someone mentioned the mainly rear end water leaks which affect all the triplets, so just check the boot, pull the carpet and check spare wheel well, manufacturers don't seem to learn, cos my Ford Mondeo Mk2 suffered the same 20 years ago, had paddling pool in the spare wheel well, sealing rear lights sorted that!
Also, the kind of mileages you looking at 90K/100K these engines often start using more oil could be piston rings or valve stem seals, but to be fair know many owners hit mileages of 150K+ and more, so they soldier on, but just thought mention it. To be fair it really a city car, so for me engine not really designed to do galactic mileages, but it refreshing to see it can.