Depending on how you plan to use, consider NOT having an AIO that includes FAX. I expect to send FAXes infrequently, and receive them even less often. So I got a Canon Pixma MP500 that does printing, scanning and photo printing well. And separately I bought a simple internal FAX modem cheap. Overall that's cheaper than a full AIO unit.
To send a FAX I will have to scan and FAX in a two-step operation; to receive I'll actually have to start a FAX software app. And, of course, none of this can be done unless the computer is running, whereas a true AIO unit can handle FAX send/receive all by itself at any time, irrespective of the computer's state. Most can even store received FAXes until you tell it to download the file into your computer, if that's what you need.
It all depends on what you will need to do.