Auto focus helps in achieving sharper, clearer and better focussed images. It is especially useful when macro shooting or shooting a subject from a close distance (<20cm). Thus cameras having auto focus have a 'clear' advantage over their non auto focus counterparts.
K750i and W810i both have auto focus and W700i doesn't. Hence the former two phones can capture much better quality image. Thats not saying W700i camera is bad. But it doesn't compare with the other two. Images captured from the camera of W700i looked decent to me. However K750i and W810i can capture exceptional quality images, going beyond what you might assume a mobile phone camera is capable of.
